Create symlinks to test artifacts for pytest runner

While temporary directories are useful for test execution to keep everything clean, they are difficult to work with manually. Create a symlink for each test artifact directory with a stable and predictable path. The symlink always either points to the latest artifacts, or is missing in case the last run succeeded.

Ensure these symlinked directories aren't detected as test suites by the pytest runner.

Closes #4252 (closed)

Related #3810