fix: fix java-cloud-bom README update workflow after monorepo migration

[suztomo]

Fixes b/537369259

Context

After the monorepo migration (PR #13498), the java-cloud-bom repository was moved into the java-cloud-bom/ subdirectory. The GitHub Actions workflow .github/workflows/java-cloud-bom-update-readme-table.yaml was copied over from the split repository without updating its paths or filter triggers.

Root Causes

1. Path-Filter Always Skips on Release Events: On a release event, dorny/paths-filter compares the release tag commit against main. Since release commits are already merged to main prior to tagging, the diff is empty, causing dorny/paths-filter to evaluate to false and skip the update-readme job.
2. Missing Working Directory: The workflow attempted to run python libraries-bom-table-generation/updateREADMETable.py from the repository root, but both the script and target README.md are located within the java-cloud-bom/ subdirectory.

Fix

• Removed redundant filter job: Replaced it with a direct job condition:

  if: ${{ github.event_name == 'workflow_dispatch' || startsWith(github.event.release.tag_name, 'libraries-bom/') }}

  This matches the release tag pattern (libraries-bom/v*) used by create_additional_release_tag.yaml and java-cloud-bom-release-note-generation.yaml.
• Configured Working Directory: Added defaults.run.working-directory: java-cloud-bom to the update-readme job so all steps execute inside java-cloud-bom/.

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.