Run 'test-stylo' on Windows CI

This likely fails to link:
rust-lang/rust#44603 (comment)

Author: SimonSapin

etc/ci/buildbot_steps.yml

@@ -146,6 +146,7 @@ windows-msvc-dev:
   - mach.bat test-unit
   - mach.bat package --dev
   - mach.bat build-geckolib
+  - mach.bat test-stylo
 
 windows-msvc-nightly:
   - mach.bat clean-nightlies --keep 3 --force