delete_untagged_containers.yml: only run on OSGeo/GDAL repository

Author: rouault

.github/workflows/delete_untagged_containers.yml

@@ -14,6 +14,7 @@ jobs:
   delete-untagged-containers:
     name: Delete all containers from gdal-deps without tags
     runs-on: ubuntu-latest
+    if: github.repository == 'OSGeo/gdal'
     steps:
     - name: Delete all containers from gdal-deps without tags
       uses: Chizkiyahu/delete-untagged-ghcr-action@bbbab219998078a91c9b283dac9389b825894603 # v3.2.0