CI: shared-files test no longer depends on GITHUB_REPOSITORY

[bernardladenthin]

Summary

• Fixes test_sibling_differences_are_warnings_not_failures in the shared .github/buildcheck/tests/test_sharedfiles.py. Since it was added on 2026-09-30, it has been red in BitcoinAddressFinder's CI only: Shared files + build checks, for example run 37680715063.
• Cause: main() never fetches the repository being checked, and it takes that name from GITHUB_REPOSITORY. The test expects the sibling it leaves unreachable, BitcoinAddressFinder, to produce a could not read … warning. In BitcoinAddressFinder's own CI that sibling is the current repository and is skipped, so the warning never appeared. Locally (GITHUB_REPOSITORY unset) and in the other three repos the test passed.
• Fix: the test pins current_repo to java-llama.cpp, the same way the other tests in the file already mock it, and additionally asserts that the pinned repository is not fetched.
• It is a shared file: the copy is byte-identical in all four repos, and every manifest hash is refreshed.

Test plan

• Reproduced: GITHUB_REPOSITORY=x/BitcoinAddressFinder python3 -m unittest discover -s .github/buildcheck/tests -t .github fails before the fix and passes after it.
• In each repo the full buildcheck suite passes under its own repository name.
• check-shared-files.py reports 0 files changed here alone, with the same hash in all four repos.
• CI is green on this branch.

Related issues / PRs

The same change is made in java-llama.cpp, BitcoinAddressFinder, streambuffer and srcmorph.

Checklist

• I have read CONTRIBUTING.md and CODE_OF_CONDUCT.md
• My commits follow Conventional Commits. They use the repository's usual CI: prefix instead.
• No security-sensitive changes

🤖 Generated with Claude Code

https://claude.ai/code/session_01AytmJF9faEiQEVt6eetQS2

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Generated by Claude Code

[claude]

✅ Review approved

This PR successfully fixes the flaky test that was failing in BitcoinAddressFinder's CI. The fix correctly isolates the test from the GITHUB_REPOSITORY environment variable by pinning current_repo via mock.patch.object(), matching patterns already established in RepoEntryTest.

Key observations:

• mock module properly imported (line 10)
• Mocking pattern consistent with existing tests
• Defensive assertion added (assertNotIn java-llama.cpp) strengthens test verification
• SHA-256 hash verified and correct
• Comment explains the issue context clearly

No issues found — code quality, security, and correctness are all solid.