ci: Functional tests for PRs in Windows GHA job stopped working

[hebasto]

During transition of the Windows runner image from version 20240122.1.0 to 20240128.1.0, the "Run functional tests" step in the "Win64 native" job stopped working for pull requests:

WARNING! Test '' not found in full test list.
No valid test scripts specified. Check that your test is in one of the test lists in test_runner.py, or run test_runner.py with no arguments to run all tests

It seems, that the empty value of the TEST_RUNNER_EXTRA environment variable is not handled properly.

[hebasto]

Cross-posting from #29581 (comment):

The breaking change was introduced in PowerShell 7.3:

Windows and Linux/macOS have fundamental differences in how native command arguments are handled specifically when quotes are involved. We added a new feature $PSNativeCommandArgumentPassing to control how PowerShell passes arguments to native commands. The default behavior for Windows and Linux/macOS should work as most users expect in their respective environments.

tl;dr: Empty strings are preserved as arguments now.

The CI was broken due to the PowerShell upgrade from 7.2.18 to 7.4.1.