tests: Skip the header tests when building on windows

The tests require having sed available and assumes that forward
slash is the path separator. The tests probably work fine within
msys like environments, but not when running plain meson/ninja in
a regular windows cmd shell.

Not sure if there's any way of checking the kind of shell that
meson executes in for a more precise check.
36 jobs for header-test-windows in 5 minutes and 17 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Style
passed #450024
amd64 docker
style-check

00:00:16

passed #450025
amd64 docker
x86inc-check

00:00:17

 
  Build
passed #450036
amd64 docker
build-android-aarch64

00:00:19

passed #450035
amd64 docker
build-android-armv7

00:00:19

passed #450026
amd64 avx2 docker
build-debian

00:00:32

passed #450037
aarch64 docker
build-debian-aarch64

00:01:10

passed #450038
aarch64 docker
build-debian-aarch64-clang-5

00:00:57

passed #450205
docker armv7
build-debian-armv7

00:00:52

passed #450206
docker armv7
build-debian-armv7-clang-5

00:00:44

passed #450029
amd64 docker
build-debian-examples

00:00:28

passed #450044
ppc64le docker
build-debian-ppc64le

00:01:04

passed #450027
amd64 docker
build-debian-static

00:00:32

passed #450040
aarch64 docker
build-debian-werror

00:00:36

passed #450028
amd64 docker
build-debian32

00:00:32

passed #450039
macos
build-macos

00:00:43

passed #450045
amd64 docker
build-pages

00:00:15

passed #450043
amd64 docker
build-ubuntu-snap

00:00:28

passed #450033
amd64 docker
build-win-arm32

00:00:19

passed #450034
amd64 docker
build-win-arm64

00:00:19

passed #450030
amd64 docker
build-win32

00:00:40

passed #450031
amd64 docker
build-win32-unaligned-stack

00:00:36

passed #450032
amd64 docker
build-win64

00:00:58

failed #450041
armv7 docker
build-debian-armv7

failed #450042
armv7 docker
build-debian-armv7-clang-5

 
  Test
passed #450046
amd64 docker
test-debian

00:00:53

98.0157%
passed #450055
aarch64 docker
test-debian-aarch64

00:02:08

passed #450057
armv7 docker
test-debian-armv7-clang-5

00:00:55

passed #450051
amd64 docker
test-debian-asan

00:01:29

passed #450047
avx2 amd64 docker
test-debian-asm

00:00:54

passed #450052
amd64 docker
test-debian-msan

00:00:54

passed #450049
amd64 docker
test-debian-mt

00:00:47

passed #450056
ppc64le docker
test-debian-ppc64le

00:02:01

passed #450053
amd64 docker
test-debian-ubsan

00:00:59

passed #450050
amd64 avx2 docker
test-debian-unaligned-stack

00:00:38

passed #450048
avx2 amd64 docker
test-debian32-asm

00:00:56

passed #450054
amd64 avx2 docker
test-win64

00:01:00