Extensions with DLL dependencies are not properly tested

[cmb69]

It seems that when running the tests of a built extension, deps\bin in not in the PATH, so extensions which require installed dependency DLLs can't be loaded while running the tests which may cause all tests to be skipped, thus silently succeeding the test run.

See e.g. https://github.com/krakjoe/parallel/actions/runs/12315528855/job/34373969013?pr=336#step:4:264.

That might have a totally different cause; I'm merely guessing that deps\bin is missing from the PATH.