tests: Enable unit test on Windows

Allow run some unit tests on Windows.
* Remove hardcoded path separator in whitelist env for Meson to choose
  OS-specific separator automatically (i.e., ';' for windows and ':' for *nix)
* Add dependency explicitly for some test cases, otherwise plugins couldn't be
  loaded on uninstalled environment of Windows.
6 jobs for windows-unittest in 33 minutes and 5 seconds (queued for 14 minutes and 58 seconds)
Status Job ID Name Coverage
  Preparation
passed gst indent #66781

00:00:33

passed manifest #66780

00:00:22

 
  Build
passed build fedora x86_64 #66782

00:03:49

 
  Test
passed check fedora #66783

00:16:51

 
  Full Builds
passed build android arm64 api28 #66784

00:02:21

passed build cerbero fedora x86_64 #66785

00:11:28