"Git not found:" message in Checkpoint Settings ends with a dangling colon and no additional detail

Steps to reproduce:

1. Create or open a project
2. Install AI Tools (AI > Install AI Tools)
3. Click "Revoke Access" in the "New MCP Connection" window
4. Open Preferences (Unity > Settings > AI > Assistant)
5. Scroll to the "Checkpoints Settings"
6. Select "Custom" in the "Select git instance"
7. Leave "Git Path" empty (or point it to an invalid location)
8. Observe the warning banner below

Actual results: The banner reads "Git not found:" - a colon with nothing following it, as if additional detail (e.g. the path that was checked) was meant to be appended but is missing.

Expected results: The message should either include the relevant detail after the colon (e.g. the invalid path), or drop the trailing colon entirely if no additional detail is intended (e.g. "Git not found.").

Reproducible with versions: 2.17.0-pre.1 (6000.0.80f1, 6000.6.0b8), 2.18.0-pre.2 (6000.3.23f1, 6000.5.7f1, 6000.7.0a5)

Tested on (OS): MacBook Pro - Tahoe 26.6.1