CI: Avoid htz4 runner for VS2019

The htz4 runner needs to be updated in order for our support binaries
like Chocolatey to work. Temporarily restrict jobs to the EC2 runner
until this has happened.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4371>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4371>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index c9c4f8f..e46b5dc 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -214,6 +214,7 @@
     - windows
     - shell
     - "1809"
+    - mesa
   script:
     - .\.gitlab-ci\windows\mesa_container.ps1 $CI_REGISTRY $CI_REGISTRY_USER $CI_REGISTRY_PASSWORD $WINDOWS_IMAGE $WINDOWS_UPSTREAM_IMAGE