ci: restore sdk-platform-java jobs (#12813)

This pull request resolves an API compatibility issue in the
`sdk-platform-java` standalone Bazel build by updating the dependency
pointers for `google-auth-library`.

## Problem
Bazel integration tests for `sdk-platform-java` were failing due to a
mismatch between local source code usage and external dependency
signatures:

```
external/com_google_api_gax_java/gax/src/main/java/com/google/api/gax/rpc/ClientContext.java:357: error: incompatible types: String cannot be converted to URI
    return ((GdchCredentials) credentials).createWithGdchAudience(audienceString);
                                                                  ^
```

This occurred because `gax-java` locally relies on
`createWithGdchAudience(String)`, which was introduced in newer versions
of `google-auth-library`, but the inner Bazel `dependencies.properties`
file was still downloading `1.42.1`.

## Solution
- Updated `google-auth-library-oauth2-http` and
`google-auth-library-credentials` versions from `1.42.1` to `1.46.0`
inside `sdk-platform-java/gax-java/dependencies.properties`.
- Added a temporary CI trigger to ensure standalone validation jobs are
correctly integrated into the main pipeline feedback cycle.

Author: diegomarquezp

.github/workflows/sdk-platform-java-ci.yaml

@@ -18,6 +18,7 @@ jobs:
           library:
             - 'sdk-platform-java/**'
             - 'google-auth-library-java/**'
+            - '.github/workflows/ci.yaml'
   build:
     needs: filter
     if: ${{ needs.filter.outputs.library == 'true' }}

sdk-platform-java/gax-java/dependencies.properties

@@ -37,8 +37,8 @@ version.io_grpc=1.76.2
 #   2) Replace all characters which are neither alphabetic nor digits with the underscore ('_') character
 maven.com_google_api_grpc_proto_google_common_protos=com.google.api.grpc:proto-google-common-protos:2.63.2
 maven.com_google_api_grpc_grpc_google_common_protos=com.google.api.grpc:grpc-google-common-protos:2.63.2
-maven.com_google_auth_google_auth_library_oauth2_http=com.google.auth:google-auth-library-oauth2-http:1.42.1
-maven.com_google_auth_google_auth_library_credentials=com.google.auth:google-auth-library-credentials:1.42.1
+maven.com_google_auth_google_auth_library_oauth2_http=com.google.auth:google-auth-library-oauth2-http:1.46.0
+maven.com_google_auth_google_auth_library_credentials=com.google.auth:google-auth-library-credentials:1.46.0
 maven.io_opentelemetry_opentelemetry_api=io.opentelemetry:opentelemetry-api:1.51.0
 maven.io_opentelemetry_opentelemetry_context=io.opentelemetry:opentelemetry-context:1.51.0
 maven.io_opencensus_opencensus_api=io.opencensus:opencensus-api:0.31.1