Fix unchecking theme overrides not creating an undo action

[YeldhamDev]

Before, unchecking a theme override in the inspector didn't create an undo action, which meant the possibility of losing it if you're not careful.

Fixes #55455.

[KoBeWi]

Does it fix #55455?

[YeldhamDev]

It does. Didn't the see the report, issue linked.

[KoBeWi]

Tested and it doesn't. It only handles the case where the checkbox is disabled, not enabled.

[YeldhamDev]

Alright, try again.

[KoBeWi]

Now there is undoredo for both, but after you undo, the action might not register.

godot.windows.editor.dev.x86_64_EXX87bq7XM.mp4

Also, sometimes the checkbox can't be clicked (it has no effect). Might be related to the above.

[YeldhamDev]

Can you tell me the order of events step-by-step? I'm unable to reproduce your issues.

[KoBeWi]

Ok this is caused by operation merging. If you toggle multiple times too fast, some toggles will be skipped from undo. This is not something that would normally happen, so it's probably fine.

The unclickable checkbox might be caused by tooltips, so also unrelated.

[YeldhamDev]

Ok this is caused by operation merging. If you toggle multiple times too fast, some toggles will be skipped from undo. This is not something that would normally happen, so it's probably fine.

This seems to happen to all toggleable properties, so not related to my PR.

The unclickable checkbox might be caused by tooltips, so also unrelated.

Suspected as much, but just wanted to be sure.

[akien-mga]

Thanks!