How to reproduce:
1. Open the attached “IN-96155” project
2. Open the “Tags & Layers” tab (Edit > Project Settings > Tags and Layers)
3. In the Tags section, click the “+” button in the bottom-right corner
4. In the opened field, input “TestTag”
5. Press Enter or click the “Save” button located under the same field
6. Observe the results

Expected result: The tag is not added to the list of tags, and a notification appears either on-screen or in the Console, indicating that the name is already taken
Actual result: The tag is not added to the list of tags, but no error message or notification is displayed

Reproducible in: 2022.3.59f1, 6000.0.41f1, 6000.1.0b9, 6000.2.0a6

Reproducible on: Windows 11
Not reproducible on: No other environments tested

Notes:
- The issue also occurs when trying to assign a new tag with the same name as a built-in Unity tag
- The issue persists across both methods of adding a new tag:
• Through the “Tags and Layers” tab in the Project Settings window
• Via the “Tags & Layers” tab in the Inspector by selecting “Add Tag…” at the bottom of the dropdown list within the Tag field of any GameObject