Adding a new item to the _MimeType picklist causes a MySQL error

[grantfitzsimmons]

Describe the bug
Adding a new value to a system pick list (like _MimeType) seems to produce a crash due to the MySQL backend not supporting timezone-aware datetimes when USE_TZ is False.

To Reproduce
Steps to reproduce the behavior:

1. Go to any app resource
2. Click on the pencil next to the name
3. Start typing any value into the Mime Type field
4. Click "+ Add"
   
5. Click "Add" in the "Add to Pick List?" dialog (Add value "yourvalue" to the Pick List named "_MimeType"?)
6. See the crash

{"exception": "ValueError", "message": "MySQL backend does not support timezone-aware datetimes when USE_TZ is False.",

Specify 7 Crash Report - 2026-08-31T16_19_46.548Z.txt

Encountered in v7.12.1

Expected behavior
It shouldn't let you add a value to this pick list, and it shouldn't crash.