Add test coverage for PropertyGrid

[MelonWang1]

Related https://github.com/dotnet/winforms/issues/10453

Proposed changes

• Add unit tests for PropertyGrid to test its events: SelectedGridItemChanged, PropertyTabChanged.

• Add unit tests for PropertyGridToolStripAccessibleObject to test its methods: Name.

  Microsoft Reviewers: Open in CodeFlow

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 98.11321% with 1 line in your changes missing coverage. Please review.

Project coverage is 74.47660%. Comparing base (dd6025d) to head (d7fca12). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #11587 +/- ## =================================================== + Coverage 74.42978% 74.47660% +0.04682% =================================================== Files 3039 3039 Lines 629056 629109 +53 Branches 46834 46837 +3 =================================================== + Hits 468205 468539 +334 + Misses 157501 157219 -282 - Partials 3350 3351 +1 ``` | [Flag](https://app.codecov.io/gh/dotnet/winforms/pull/11587/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | Coverage Δ | | |---|---|---| | [Debug](https://app.codecov.io/gh/dotnet/winforms/pull/11587/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `74.47660% <98.11321%> (+0.04682%)` | :arrow_up: | | [integration](https://app.codecov.io/gh/dotnet/winforms/pull/11587/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `17.98580% <ø> (+0.08332%)` | :arrow_up: | | [production](https://app.codecov.io/gh/dotnet/winforms/pull/11587/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `47.34857% <ø> (+0.09928%)` | :arrow_up: | | [test](https://app.codecov.io/gh/dotnet/winforms/pull/11587/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `96.95252% <98.11321%> (-0.00011%)` | :arrow_down: | | [unit](https://app.codecov.io/gh/dotnet/winforms/pull/11587/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `44.33195% <ø> (+0.01402%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet#carryforward-flags-in-the-pull-request-comment) to find out more.