tests: info: fix post init cat reg test on windows and with CK_FORK=no
tests: info: fix post init cat reg test on windows and with CK_FORK=no

The test checks that categories not covered by the pattern in the
GST_DEBUG string have debug level GST_LEVEL_DEFAULT set, but previous
tests mess with the default threshold, which made this test fail on
Windows or when run with CK_FORK=no. Fix this by resetting everything
at the beginning, and then also do a sanity check afterwards.

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer