feat: avoid aync validation conflicts

[anchenyi]

https://msazure.visualstudio.com/Microsoft%20Teams%20Extensibility/_workitems/edit/27132725

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.90909% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 87.26%. Comparing base (654c223) to head (abbc72c). Report is 28 commits behind head on dev.

Additional details and impacted files

[](https://app.codecov.io/gh/OfficeDev/TeamsFx/pull/11229?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OfficeDev) ```diff @@ Coverage Diff @@ ## dev #11229 +/- ## ========================================== + Coverage 87.24% 87.26% +0.02% ========================================== Files 458 458 Lines 27903 27953 +50 Branches 5613 5622 +9 ========================================== + Hits 24343 24393 +50 Misses 1788 1788 Partials 1772 1772 ``` | [Files](https://app.codecov.io/gh/OfficeDev/TeamsFx/pull/11229?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OfficeDev) | Coverage Δ | | |---|---|---| | [...src/component/driver/teamsApp/validateTestCases.ts](https://app.codecov.io/gh/OfficeDev/TeamsFx/pull/11229?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OfficeDev#diff-cGFja2FnZXMvZngtY29yZS9zcmMvY29tcG9uZW50L2RyaXZlci90ZWFtc0FwcC92YWxpZGF0ZVRlc3RDYXNlcy50cw==) | `95.86% <90.90%> (-0.50%)` | :arrow_down: | ... and [6 files with indirect coverage changes](https://app.codecov.io/gh/OfficeDev/TeamsFx/pull/11229/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OfficeDev)

[anchenyi]

If a user submits another async validation request while the previous one is still in progress, a warning will be shown in the output, and the second submission will be cancelled.