Upgrade from Drupal does not set image_toolkit config value

[indigoxela]

Description of the bug

In new installs the image_toolkit setting ships with core/modules/system/config/system.core.json, but when upgrading, this value is never set.

Steps To Reproduce

1. Upgrade from Drupal 7
2. Inspect your active config json

Actual behavior

No setting for image_toolkit in system.core.json

Expected behavior

I'd expect an upgrade to have all config items, that new installs have.

Additional information

• Backdrop CMS version: latest 1.x dev
• PHP version: 8.5 - where this will cause some problems

Discovered while working on #7008, but the problem has always been there.
My suspicion is, that more config items might be missing, but that needs more research.