fix: make SARIF upload graceful when code scanning unavailable

Add continue-on-error to the CodeQL upload-sarif step so the
workflow doesn't fail if GitHub Advanced Security code scanning
isn't enabled or accessible.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mchmarny

.github/actions/security-scan/action.yml

@@ -75,3 +75,4 @@ runs:
       with:
         sarif_file: ${{ inputs.output_file }}
         category: ${{ inputs.category }}
+      continue-on-error: true  # Don't fail if code scanning is unavailable