Revert "ci: Disable Windows for now"

This reverts commit be385ab5bc.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14975>

.gitlab-ci.yml

@@ -589,7 +589,7 @@ debian/arm_test:
   script:
     - .\.gitlab-ci\windows\mesa_container.ps1 $CI_REGISTRY $CI_REGISTRY_USER $CI_REGISTRY_PASSWORD $MESA_IMAGE $MESA_UPSTREAM_IMAGE ${DOCKERFILE} ${MESA_BASE_IMAGE}
 
-.windows_build_vs2019:
+windows_build_vs2019:
   inherit:
     default: false
   extends:
@@ -600,7 +600,7 @@ debian/arm_test:
     DOCKERFILE: Dockerfile_build
   timeout: 2h 30m # LLVM takes ages
 
-.windows_test_vs2019:
+windows_test_vs2019:
   inherit:
     default: false
   extends:
@@ -1079,7 +1079,7 @@ debian-clang:
     CC: clang
     CXX: clang++
 
-.windows-vs2019:
+windows-vs2019:
   extends:
     - .build-windows
     - .use-windows_build_vs2019