chore: add a presubmit that checks for librarian config consistency

Currently we're using librarian for generation and legacylibrarian for
releasing. This check makes sure that the relevant aspects of the two
configurations (which libraries are configured, their versions, and
whether releases are blocked) are consistent.

This commit also ensures that we're starting from a consistent state.

Author: jskeet

.github/workflows/librarian_config_check.yml

@@ -0,0 +1,40 @@
+name: check that Librarian and legacylibrarian configs are consistent
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+permissions:
+  contents: read
+jobs:
+  config-check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+      # Use this action, rather than a file filter so that we can make this
+      # mandatory.
+      # See https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#example-including-branches
+      # for more details.
+      - uses: dorny/paths-filter@v4
+        id: filter
+        with:
+          filters: |
+            librarian:
+              - 'librarian.yaml'
+              - '.librarian/config.yaml'
+              - '.librarian/state.yaml'
+      - name: Config check
+        if: steps.filter.outputs.librarian == 'true'
+        run: |
+          V="$(sed -n 's/^version: *//p' librarian.yaml)"
+          go run "github.com/googleapis/librarian/tool/cmd/configcheck@${V}" .
+      - name: Update library versions and regenerate
+        if: failure()
+        run: |
+          echo "Library configuration is different between state.yaml and librarian.yaml.
+          Update library configuration in the configs according to the error message and
+          regenerate libraries using:
+          
+          V=\$(sed -n 's/^version: *//p' librarian.yaml)
+          go run github.com/googleapis/librarian/cmd/librarian@\${V} generate --all
+          "

librarian.yaml

@@ -55,6 +55,7 @@ default:
 libraries:
   - name: bigframes
     version: 2.39.0
+    skip_release: true
     python:
       library_type: INTEGRATION
   - name: bigquery-magics
@@ -1933,6 +1934,7 @@ libraries:
     version: 3.10.1
     apis:
       - path: google/storage/v2
+    skip_release: true
     python:
       library_type: GAPIC_MANUAL
       opt_args_by_api:
@@ -2194,6 +2196,7 @@ libraries:
       default_version: v1
   - name: google-crc32c
     version: 1.8.0
+    skip_release: true
     python:
       library_type: OTHER
   - name: google-geo-type