Unstable unit test: System.Windows.Forms.Tests.ClipboardTests.Clipboard_SetText_InvokeStringTextDataFormat_GetReturnsExpected(format: Text)

Related #11227

### Test

System.Windows.Forms.Tests.ClipboardTests.Clipboard_SetText_InvokeStringTextDataFormat_GetReturnsExpected(format: Text)

### Issue description

The failure scenario:

System.Windows.Forms.Tests.ClipboardTests.Clipboard_SetText_InvokeStringTextDataFormat_GetReturnsExpected(format: Rtf)

**Error Message:**

- **In X64 unit:**
- Expected string to be "text" with a length of 4, but "" has a length of 0, differs near "" (index 0).

**Stack trace:**

```
at FluentAssertions.Execution.XUnit2TestFramework.Throw(String message)
at FluentAssertions.Execution.TestFrameworkProvider.Throw(String message)
at FluentAssertions.Execution.DefaultAssertionStrategy.HandleFailure(String message)
at FluentAssertions.Execution.AssertionScope.FailWith(Func`1 failReasonFunc)
at FluentAssertions.Primitives.StringEqualityValidator.ValidateAgainstLengthDifferences()
at FluentAssertions.Primitives.StringValidator.Validate()
at FluentAssertions.Primitives.StringAssertions`1.Be(String expected, String because, Object[] becauseArgs)
at System.Windows.Forms.Tests.ClipboardTests.Clipboard_SetText_InvokeStringTextDataFormat_GetReturnsExpected(TextDataFormat format) in /_/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ClipboardTests.cs:line 506
at InvokeStub_ClipboardTests.Clipboard_SetText_InvokeStringTextDataFormat_GetReturnsExpected(Object, Span`1)
at System.Reflection.MethodBaseInvoker.InvokeWithOneArg(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
```