tests: Enable test generic_states on Windows

... and drop needless unistd.h dependency
6 jobs for ugly-tests-windows in 29 minutes and 9 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #70598
gst indent

00:00:27

passed #70597
manifest

00:00:35

 
  Build
passed #70599
build fedora x86_64

00:06:54

 
  Test
passed #70600
check fedora

00:14:40

 
  Full Builds
passed #70601
build android arm64 api28

00:02:52

passed #70602
build cerbero fedora x86_64

00:06:58