CI: limit kms test runs to upstream repo

* tests can only pass if the KMS allows the repository to authenticate
* even the failure will fail on a fresh clone as the issue filing fails
  by default (as issues are not enabled)

Author: jku

.github/workflows/test-kms.yml

@@ -9,6 +9,7 @@ permissions: {}
 jobs:
   test-kms:
     runs-on: ubuntu-latest
+    if: github.repository_owner == 'secure-systems-lab' # only run upstream
 
     permissions:
       id-token: 'write' # for OIDC auth for GCP authentication