"NullReferenceException" and ""GUI Error: Invalid GUILayout" errors when clicking "Run Selected" in Test Runner with no tests visible in search results

Steps to reproduce:

1. Create a new 3D URP project
2. Import into the assets folder the attached "TestRunnerRepro" (any tests will work for reproduction)
3. Open Window > General > Test Runner 
4. Select any test
5. In the search field type in any text so no matches are returned
6. Observe the "Run Selected" button is still active and click on it
7. Observe the Console

Actual results: "NullReferenceException: Object reference not set to an instance of an object
UnityEditor.TestTools.TestRunner.GUI.TestListGUI+<>c.<ConstructFilter>b__78_1" and "GUI Error: Invalid GUILayout state in TestRunnerWindow view. Verify that all layout Begin/End calls match" errors are thrown

Expected results: No errors and "Run Selected" button should be disabled or prevented from causing errors

Reproducible with versions: 6000.0.0f1, 6000.3.16f1, 6000.4.9f1, 6000.5.0b10, 6000.6.0a6

Tested on (OS): Ubuntu 24.04, macOS 26.5