How to solve "TextMate is running on a read-only file system and can therefore not be updated."

When using Textmate, I'm regularly prompted to upgrade: > TextMate 2.0.23 is now available. You have version 2.0.19. Would you like to download it now? However, if I choose the upgrade option, I immediately see a dialog with this error: > TextMate is running on a read-only file system and can therefore not be updated. > > If you downloaded TextMate from the internet then moving it out of the Downloads folder should solve the problem. Textmate isn't in my Downloads folder; it's in /Applications. Its permissions look like this:

drwxr-xr-x@  3 sam   staff    96 15 Feb  2021 TextMate.app

It wasn't installed via brew, so upgrading it that way isn't an option. How could I do an upgrade? Is removing the app and reinstalling it the only way? I'm on MacOS Catalina 10.15.7 (19H1519).