Unstable unit test: System.Windows.Forms.UITests.ButtonTests.Button_DialogResult_SpaceToClickFocusedButtonAsync

Related #11227

### Test

System.Windows.Forms.UITests.ButtonTests.Button_DialogResult_SpaceToClickFocusedButtonAsync

### Issue description

**The case failed in X64 unit tests, the failure link:**

- [ #20240427.4 • [main] Update dependencies from dotnet/runtime (#11281)](https://dev.azure.com/dnceng-public/public/_build/results?buildId=658065&view=ms.vss-test-web.build-test-results-tab&runId=16298392&resultId=119204&paneView=debug)
- [#20240430.11 • Enable nullability in DesignerWindowTarget (#11279)](https://dev.azure.com/dnceng-public/public/_build/results?buildId=661041&view=ms.vss-test-web.build-test-results-tab)

**Failed scenario:**
- System.Windows.Forms.UITests.ButtonTests.Button_DialogResult_SpaceToClickFocusedButtonAsync

**Error Message:**

- **In X64 unit:**
- Assert.Equal() Failure: Values differ
Expected: OK
Actual: None

**Stack trace:**
```
at System.Windows.Forms.UITests.ButtonTests.b__2_0(Form form, Button button) in /_/src/System.Windows.Forms/tests/IntegrationTests/UIIntegrationTests/ButtonTests.cs:line 67
at System.Windows.Forms.UITests.ControlTestBase.<>c__DisplayClass32_0`1.<b__0>d.MoveNext() in /_/src/System.Windows.Forms/tests/IntegrationTests/UIIntegrationTests/Infra/ControlTestBase.cs:line 315
--- End of stack trace from previous location ---
at Microsoft.VisualStudio.Threading.JoinableTask.JoinAsync(CancellationToken cancellationToken)
at System.Windows.Forms.UITests.ControlTestBase.RunFormAsync[T](Func`1 createDialog, Func`3 testDriverAsync) in /_/src/System.Windows.Forms/tests/IntegrationTests/UIIntegrationTests/Infra/ControlTestBase.cs:line 339
at System.Windows.Forms.UITests.ControlTestBase.RunSingleControlTestAsync[T](Func`3 testDriverAsync, Func`1 createControl, Func`1 createForm) in /_/src/System.Windows.Forms/tests/IntegrationTests/UIIntegrationTests/Infra/ControlTestBase.cs:line 246
at System.Windows.Forms.UITests.ButtonTests.RunTestAsync(Func`3 runTest) in /_/src/System.Windows.Forms/tests/IntegrationTests/UIIntegrationTests/ButtonTests.cs:line 385
at System.Windows.Forms.UITests.ButtonTests.Button_DialogResult_SpaceToClickFocusedButtonAsync() in /_/src/System.Windows.Forms/tests/IntegrationTests/UIIntegrationTests/ButtonTests.cs:line 57
--- End of stack trace from previous location ---
```