Don't add cwd argument when running all tests

[bhrutledge]

Follow-up to #17622 and #17898, attn: @karthiknadig.

I tested this using my example workspace with "python.testing.cwd" set to a sub-directory, and testpaths in pytest.ini set to a sub-directory of that.

Before this change, running all tests yields:

Running tests (pytest): /Users/bhrutledge/Dev/vscode-pytest-workspace/repo/rootdir
Running test with arguments: --rootdir /Users/bhrutledge/Dev/vscode-pytest-workspace/repo/rootdir --override-ini junit_family=xunit1 --junit-xml=/var/folders/bw/ttgk1hcs0k989q2yzmxkzn8c0000gp/T/tmp-69875H3gF3f2niW84.xml /Users/bhrutledge/Dev/vscode-pytest-workspace/repo/rootdir
Current working directory: /Users/bhrutledge/Dev/vscode-pytest-workspace/repo/rootdir
Workspace directory: /Users/bhrutledge/Dev/vscode-pytest-workspace
Run completed, parsing output
Test result not found for: ./package/test_module.py::test_function

This is because the cwd is appended as an argument, which causes pytest to ignore testpaths, which causes it to collect tests that it shouldn't, causing a collection error.

With this change, running all tests yields:

Running tests (pytest): /Users/bhrutledge/Dev/vscode-pytest-workspace/repo/rootdir
Running test with arguments: --rootdir /Users/bhrutledge/Dev/vscode-pytest-workspace/repo/rootdir --override-ini junit_family=xunit1 --junit-xml=/var/folders/bw/ttgk1hcs0k989q2yzmxkzn8c0000gp/T/tmp-71331owgO7UMfr1MG.xml
Current working directory: /Users/bhrutledge/Dev/vscode-pytest-workspace/repo/rootdir
Workspace directory: /Users/bhrutledge/Dev/vscode-pytest-workspace
Run completed, parsing output
./package/test_module.py::test_function Passed

Note that cwd is no longer an argument.

It looks cwd defaults to workspaceFolder.fsPath, so this seems like a safe change.