fix(ci): quote store:: test filter so db-checks.yml parses on GitHub

The unquoted trailing '::' in 'cargo test --lib store::' is invalid
plain-scalar YAML in block context, so GitHub rejected the entire
workflow at parse time: startup_failure, zero jobs, no check run.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/db-checks.yml

@@ -125,7 +125,7 @@ jobs:
           echo "repositories columns OK ✓"
 
       - name: Store-layer round-trip tests
-        run: cargo test --lib store::
+        run: 'cargo test --lib store::'
 
       - name: Summary
         if: always()