Update source repo in BCR metadata.json (bazel-contrib#2672)

Update after bazel-contrib#2638

Author: meteorcloudy

.bcr/metadata.template.json

@@ -13,7 +13,8 @@
     }
   ],
   "repository": [
-    "github:bazelbuild/rules_python"
+    "github:bazelbuild/rules_python",
+    "github:bazel-contrib/rules_python"
   ],
   "versions": [],
   "yanked_versions": {}