Localization: "Add Custom Locale" has no tooltip, while both neighbouring buttons in the same row do

Steps to reproduce:

1. Create a new project
2. Install the Localization package (com.unity.localization)
3. Open Edit > Project Settings > Localization and click Create to make the settings asset
4. Hover "Add Locale" and wait for the tooltip
5. Hover "Add Custom Locale" and wait
6. Hover "Add All" and wait for the tooltip

Actual results: No tooltip appears for "Add Custom Locale". Both neighbours in the same row have one: "Add Locale" and "Add All". Of the three, "Add Custom Locale" is the button whose purpose is least self-evident

Expected results: All three buttons in the row carry a tooltip

Reproducible with versions: 1.5.12 (6000.5.7f1, 6000.6.0f1, 6000.7.0a6)

Tested on (OS): MacBook Pro - Tahoe 26.6.2

Notes:

• The three buttons sit side by side in one row, so the inconsistency is visible in a single screenshot with the cursor on the middle button.