Include java-build in the PR test summary

The "PR test summary (non-blocking)" job (ci/utils/pr_test_summary.py, wired up in .github/workflows/pr.yaml) only depends on and reports conda-cpp-tests, conda-python-tests, wheel-tests-cuopt, wheel-tests-cuopt-server, and test-self-hosted-server (_TEST_PREFIXES in the script, and the pr-test-summary job's needs: list). java-build isn't included, so it neither gates the summary nor shows up in it — the summary can post "all tests passed" while java-build is still running or has failed.

Possible fix

• Add java-build to pr-test-summary's needs: list in .github/workflows/pr.yaml
• Add a matching prefix to _TEST_PREFIXES in ci/utils/pr_test_summary.py
• Note: _analyze_job_log only parses gtest ([ FAILED ]) and pytest (short test summary info) failure formats. A failed java-build job would still show up correctly as a failed job in the top-line counts, just without a per-test breakdown (JUnit/Surefire output isn't parsed) — that's an acceptable degrade, not a blocker, unless we also want per-test Java failures listed.

Context

Noticed while investigating #1820 / #1823: PR #1823's "PR test summary (non-blocking)" check passed while java-build / build was still in progress, which was confusing to reviewers since it looked like the whole PR was green.