Add concurrent-ruby ReadWriteLock fixed references

[cookesan]

Adds concurrent-ruby ReadWriteLock fixed references to GHSA-6wx8-w4f5-wwcr.

Audit refresh, July 8, 2026:

• Confirmed the live PR is open, ready for review, merge-clean, and the visible advisory check is green.
• Rechecked the merge-base diff: exactly one advisory JSON file changes (advisories/github-reviewed/2026/06/GHSA-6wx8-w4f5-wwcr/GHSA-6wx8-w4f5-wwcr.json), JSON parses, git diff --check passes, and the exact-head worktree is clean.
• Revalidated the added public references and package-version evidence in the diff; all resolve through their source site or registry.

[cookesan]

Review note: this expands GHSA-6wx8-w4f5-wwcr with the concurrent-ruby v1.3.7 release and RubyGems package evidence. I checked the PR head JSON against the OSV schema, confirmed the GitHub release URL resolves, and confirmed RubyGems has concurrent-ruby 1.3.7; the affected RubyGems range, CVSS 4.0 score, alias, and package metadata stay unchanged.