[Eval > Test Suites] Test Suite validity status not revalidated after clearing a required binding

### EPAM AI DIAL Admin version

Admin: [FE]0.17.0-dev.98 [BE]0.17.0-dev.13

### How to reproduce

1. Login to Admin
2. Navigate to Evaluation > Test Suites and create a new Test Suite for a /chat/completions deployment
3. Observe that the Test Suite status shows "Invalid" (REQUIRED: Required variable 'user_message' has no binding)
4. Open the Test Cases tab, find the dynamic configuration for 'user_message', enter any value (e.g., "hello"), and save
5. Verify the Test Suite status changes to "Valid"
6. Clear the 'user_message' field and save again
7. Check the Test Suite status

### Actual result

The Test Suite status remains "Valid" despite the required variable 'user_message' having no binding.

### Expected result

The Test Suite status should revert to "Invalid" when a required binding is cleared and saved.

### Additional information

_No response_

### Confidential information

- [x] I confirm that do not share any confidential information