CI: check launchable/jar/exe_deploy.jar is up to date when src/ Java files change

[Konboi]

Why

When Java source files under src/ are updated, build-java.sh must be run to regenerate and copy exe_deploy.jar to launchable/jar/exe_deploy.jar. This step is easy to forget, and there was no CI check to catch it.

What

Added a new step to the bazel-test.yml workflow that:

• Runs only when src/ Java files change (already handled by the existing paths trigger)
• Builds the jar with Bazel
• Compares the built jar against launchable/jar/exe_deploy.jar using diff
• Fails with a clear error message if they differ, prompting the developer to run build-java.sh

Please Review Here

• The check reuses the already-built jar from the previous bazel test //... step via Bazel's cache, so the extra bazel build call should be fast.
• This PR targets v1. A separate PR will be needed for main (where the copy destination is smart_tests/jar/exe_deploy.jar instead).

[Konboi]

Tested by https://github.com/cloudbees-oss/smart-tests-cli/actions/runs/27120427952/job/81580320594#step:7:1