tests: Enable test generic_states on Windows

... and drop needless unistd.h dependency
8 jobs for master in 15 minutes and 51 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #78933
gst indent

00:00:20

passed #78932
manifest

00:00:18

 
  Build
passed #78934
build fedora x86_64

00:04:23

 
  Test
passed #78935
check fedora

00:03:25

 
  Full Builds
passed #78936
build android arm64 api28

00:03:10

passed #78938
build cerbero cross win32

00:07:30

passed #78939
build cerbero cross win64

00:07:40

passed #78937
build cerbero fedora x86_64

00:07:19