Test are not automatically refreshed after pytest installation

[karthiknadig]

Testing #21092

After opening the test repository, create environment and trigger testing. Test does not show failed output with missing pytest.

After installing pytest, it does not automatically refresh.

[eleanorjboyd]

noting this is a regression in the new testing rewrite

[eleanorjboyd]

fixed by #21133

[rzhao271]

When I start with no venv, I first create a venv Python environment. Then, I navigate to the testing panel and configure pytest tests. I then notice that pytest is installed, but the tests don't refresh, and pressing the refresh button doesn't load the tests, either.

[eleanorjboyd]

Sorry this needs tomorrow's insiders release and a specific testing constant- will switch to author verification and have @karthiknadig look at it tomorrow. Thanks!

[eleanorjboyd]

verification steps:

1. launch vscode with the environment variable ENABLE_PYTHON_TESTING_REWRITE = '1'
2. use the create environment command from the command palette, select venv and whatever python version you want >=3.7 (your environment needs to not have pytest installed so you can use an existing one but this condition just has to be met)
3. click on the test icon to pull up test discovery, check to make sure the error message looks right
4. install pytest, make sure it re-finds tests after install