Fixed broken external links

Related to: https://gitlab.com/gitlab-org/technical-writing/-/issues/492

doc/api/container_registry.md

@@ -350,7 +350,7 @@ curl --request DELETE --header "PRIVATE-TOKEN: <your_access_token>" \
 ```
 
 This action doesn't delete blobs. To delete them and recycle disk space,
-[run the garbage collection](https://docs.gitlab.com/omnibus/maintenance/README.html#removing-unused-layers-not-referenced-by-manifests).
+[run the garbage collection](https://docs.gitlab.com/omnibus/maintenance/index.html#removing-unused-layers-not-referenced-by-manifests).
 
 ## Delete registry repository tags in bulk
 
@@ -388,7 +388,7 @@ This API call performs the following operations:
 These operations are executed asynchronously and can take time to get executed.
 You can run this at most once an hour for a given container repository. This
 action doesn't delete blobs. To delete them and recycle disk space,
-[run the garbage collection](https://docs.gitlab.com/omnibus/maintenance/README.html#removing-unused-layers-not-referenced-by-manifests).
+[run the garbage collection](https://docs.gitlab.com/omnibus/maintenance/index.html#removing-unused-layers-not-referenced-by-manifests).
 
 WARNING:
 The number of tags deleted by this API is limited on GitLab.com