ci: fix scheduled security scan (#1004)

`codeql-action/upload-sarif` needs to know where the scanned code
was checked out if it has been checked out to a subdir of `github.workspace`.

Author: lavarou

.github/workflows/security-scan.yml

@@ -45,4 +45,5 @@ jobs:
         if: ${{ github.event_name == 'schedule' }}
         uses: github/codeql-action/upload-sarif@v3
         with:
+          checkout_path: ./php-agent
           sarif_file: trivy-results.sarif