Tanya Solyanik

@RutulPatel8 - please investigate test failures and take a look at another PR in TreeNodesCollection area that might be addressing this regression as well https://github.com/dotnet/winforms/pull/11253.

Please investigate the failing tests

>However, this fix conflicts with existing tests, which expect the DataGridViewRow header's left border to be set to Outset. To ensure the integrity of the codebase, I'm considering modifying the...

In this image -  the column border is not visible between the column headers. Could you please open a new issue for that?

@ricardobossan - please investigate unit test failures

@Olina-Zhang - could you please test this change when you have time?

The fact that `[CollectionDefinition("Sequential", DisableParallelization = true)]` makes a difference indicates that we have still more Clipboard tests among other test classes, because this attribute ensures that all tests within...

@paul1956 - we are moving clipboard tests into new classes, not adding them to ClipboardTests.cs file - https://github.com/dotnet/winforms/blob/34298ef4ef6d9a9c59cd344cffdaa12ece15209d/src/System.Windows.Forms/tests/UnitTests/TextBoxBaseTests.ClipboardTests.cs#L8

`@Tanya-Solyanik I think the name "Sequential" should be changed to "ClipboardSequential", "WebBrowserSequential" and any other specific shared resource.` Perhaps at some point, if we see that tests are running too...

DataObjectTests mostly work with our custom DataObject.DataStore implementation. Good point about registering the same formates across different tests. Perhaps we should enforce that each test registers format named as `nameof(test...