CI: Disable Windows build due to unstable infrastructure

The Windows runner is having a lot of issues cloning repositories,
failing early due to an unhandled HTTP error. Temporarily disable it
until we can figure out what's going on and fix it.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5716>

.gitlab-ci.yml

@@ -366,7 +366,7 @@ arm64_test:
     WINDOWS_IMAGE: "$CI_REGISTRY_IMAGE/windows/x64_build:$WINDOWS_TAG"
     WINDOWS_UPSTREAM_IMAGE: "$CI_REGISTRY/$FDO_UPSTREAM_REPO/windows/x64_build:$WINDOWS_TAG"
 
-windows_build_vs2019:
+.windows_build_vs2019:
   extends:
     - .container
     - .windows-docker-vs2019
@@ -591,7 +591,7 @@ meson-clang:
     CC: "ccache clang-9"
     CXX: "ccache clang++-9"
 
-meson-windows-vs2019:
+.meson-windows-vs2019:
   extends:
     - .build-windows
     - .use-windows_build_vs2019