Unable to add ONLY mutations to remote schema permissions

### Version Information

Server Version: 2.1.1

### What is the expected behaviour?

Should be able to select mutations when setting remote schema permissions.

### What is the current behaviour?

Completely unable to select mutations in remote schema permissions. Whether combined with queries or standalone.

### How to reproduce the issue?

1. Enable remote schema permissions
2. Go to the web console, select a remote schema and permissions
3. Expand mutation_root
4. Select any mutation
5. Click the save button at the bottom
6. Error popup in the top right

### Screenshots or Screencast