ci: update security-scanner token

The old token had expired, this is the org-wide one
we should be using.

.github/workflows/security-scan.yml

@@ -39,7 +39,7 @@ jobs:
       uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
       with:
         repository: hashicorp/security-scanner
-        token: ${{ secrets.HASHIBOT_PRODSEC_GITHUB_TOKEN }}
+        token: ${{ secrets.PRODSEC_SCANNER_READ_ONLY }}
         path: security-scanner
         ref: main