chore: update librarian to v0.23.1-0.20260701125507-b8e50a51a11c (#13619)

Update librarian version that includes:
- googleapis/librarian#6601.
- googleapis/librarian#6582 (for this change,
added a fix in README template
[7522f3b](7522f3b))

Created with command below plus a manual fix in
[7522f3b](7522f3b)
```
# update librarian version used in librarian.yaml
PSEUDO=$(GOPROXY=direct go list -m -f '{{.Version}}' github.com/googleapis/librarian@main)
V=$(go run github.com/googleapis/librarian/cmd/librarian@latest config get version)
go run github.com/googleapis/librarian/cmd/librarian@${V} config set version $PSEUDO

# regenerate all
go run github.com/googleapis/librarian/cmd/librarian@${V} generate -all
```

Fixes #13609

Author: zhumin8

java-accessapproval/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "enables controlling access to your organization's data by Google personnel.",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-cloud-accessapproval/latest/overview",
   "release_level": "stable",
-  "transport": "both",
+  "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-accessapproval",

java-accesscontextmanager/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "n/a",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-identity-accesscontextmanager/latest/overview",
   "release_level": "stable",
-  "transport": "both",
+  "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-accesscontextmanager",

java-admanager/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "The Ad Manager API enables an app to integrate with Google Ad Manager. You can read Ad Manager data and run reports using the API.",
   "client_documentation": "https://cloud.google.com/java/docs/reference/ad-manager/latest/overview",
   "release_level": "preview",
-  "transport": "http",
+  "transport": "rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-admanager",

java-advisorynotifications/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "An API for accessing Advisory Notifications in Google Cloud.",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-cloud-advisorynotifications/latest/overview",
   "release_level": "stable",
-  "transport": "both",
+  "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-advisorynotifications",

java-agentregistry/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "Agent Registry is a centralized, unified catalog that lets you store,\ndiscover, and govern Model Context Protocol (MCP) servers, tools, and AI\nagents within Google Cloud.",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-cloud-agentregistry/latest/overview",
   "release_level": "preview",
-  "transport": "both",
+  "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-agentregistry",

java-alloydb/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "AlloyDB is a fully managed, PostgreSQL-compatible database service with industry-leading performance, availability, and scale.",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-cloud-alloydb/latest/overview",
   "release_level": "stable",
-  "transport": "both",
+  "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-alloydb",

java-analytics-admin/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "allows you to manage Google Analytics accounts and properties.",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-analytics-admin/latest/overview",
   "release_level": "preview",
-  "transport": "both",
+  "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-analytics-admin",

java-analytics-data/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "provides programmatic methods to access report data in Google Analytics App+Web properties.",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-analytics-data/latest/overview",
   "release_level": "preview",
-  "transport": "both",
+  "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-analytics-data",

java-analyticshub/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "TBD",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-cloud-analyticshub/latest/overview",
   "release_level": "stable",
-  "transport": "both",
+  "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-analyticshub",

java-api-gateway/.repo-metadata.json

@@ -5,7 +5,7 @@
   "api_description": "enables you to provide secure access to your backend services through a well-defined REST API that is consistent across all of your services, regardless of the service implementation. Clients consume your REST APIS to implement standalone apps for a mobile device or tablet, through apps running in a browser, or through any other type of app that can make a request to an HTTP endpoint.",
   "client_documentation": "https://cloud.google.com/java/docs/reference/google-cloud-api-gateway/latest/overview",
   "release_level": "stable",
-  "transport": "both",
+  "transport": "grpc+rest",
   "language": "java",
   "repo": "googleapis/google-cloud-java",
   "repo_short": "java-api-gateway",