Clicking the Discard changes from the Registries screens should cancel latest changes

Steps to reproduce:

1. Go on Registries > Action categories.
2. Insert example.
3. Click on the button Discard changes.
   -> Changes are not canceled.
4. Click on any item in Studio menu to leave the Action categories screen.
   -> The unsaved changes dialog pops up.
5. Click Discard changes.
   -> Changes are canceled.

=> Clicking on the button Discard changes at step 3 should cancel the insertion of the example.