ci: update sdk-platform-java reference to google-cloud-java

[suztomo]

We moved the definition of the workflow files from sdk-platform-java repository to the sdk-platform-java folder in the google-cloud-java repository.

This uses the "latest" Docker tag in .github/workflows/hermetic_library_generation.yaml to confirm the behavior of the today's hermetic build container image update.

b/503444342

[generated-files-bot]

Warning: This pull request is touching the following templated files:

• renovate.json

[suztomo]

Trying to use the updated hermetic build container image.

[suztomo]

RenovateBot validation failure seems irrelevant

  npm install -g npm@latest
  npm install --global renovate
  renovate-config-validator
  shell: /usr/bin/bash -e {0}
npm error code MODULE_NOT_FOUND
npm error Cannot find module 'promise-retry'
npm error Require stack:
npm error - /opt/hostedtoolcache/node/22.22.2/x64/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/rebuild.js

Hermetic build no longer reverts the "googleapis/sdk-platform-java" reference (9f4a34d).

[blakeli0]

Is this needed?

[suztomo]

This is needed to specify the container image built today.

Next google-cloud-java release onwards, we don't need this.