ci: Switch msys2 job to manual

This will reduce the excessive load on the runners which are having issues
with this job in particuliar. We will revisit when we better understand the
runners issues.

gitlab/ci_template.yml

@@ -469,8 +469,13 @@ build vs2017 x86:
   variables:
     ARCH: 'x86'
 
+# Disabled until the runner issues has been resolved.
 build msys2 :
   extends: '.build windows'
+  rules:
+    - if: '$CI_PROJECT_NAME !~ /^(cerbero|gst-docs|gst-integration-testsuites|gst-omx|gst-plugins-rs|gstreamer-vaapi)$/'
+      allow_failure: true
+      when: manual
   timeout: '60min'
   script:
     # Sometimes there's seems to be an existing gst-build clone that comes either from the ether or