Add test harness

[amotl]

Dear Mathias,

thank you for aiming to improve the discovery of tests that exclusively fail on Windows within the test suite of CrateDB (crate/crate#11924). CI croaked on that because the upload process was invoked from PowerShell, so I tried to improve the situation already with crate/crate#11994.

However, there has been another incompatibility with Windows, discovered with CrateDB GHA build #4567182253. While this patch just sets the stage, #3 actually fixes it.

If you like the patch, you might want to assign a secrets.WACKLIG_TOKEN before acknowledging the CI run.

With kind regards,
Andreas.

P.S.: Other than the test harness, 51168a1 brings in a small fix related to finding test report files recursively.

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Running it on GHA's test matrix already succeeded, see wacklig-uploader GHA build #1596218664. The upload itself fails because a WACKLIG_TOKEN is not configured yet, but this currently gets ignored by using continue-on-error: true within the GHA recipe.

Test coverage is 100%.

Name                        Stmts   Miss  Cover   Missing
---------------------------------------------------------
tests/conftest.py               4      0   100%
tests/test_environment.py      41      0   100%
tests/test_uploader.py         49      0   100%
wacklig.py                     55      0   100%
---------------------------------------------------------
TOTAL                         149      0   100%