Schutzfile: fix centos-stream-9 repo pin

During runner repo override the runner name is compared with the key in
Schutzfile. There was the word 'stream' missing for centos runners so
the repos were never acutally overwritten before. See
https://github.com/osbuild/gitlab-ci-terraform-executor/blob/main/prepare#L69
for more context

Schutzfile

@@ -127,7 +127,9 @@
       "osbuild": {
         "commit": "d8f36b55fa043002c6650a75fbeba5165cc0824b"
       }
-    },
+    }
+  },
+  "centos-stream-9": {
     "repos": {
       "file": "/etc/yum.repos.d/centos.repo",
       "x86_64": [
@@ -166,4 +168,4 @@
       ]
     }
   }
-}
+}