Disable MSVC CI by default for now

The necessary CI runner doesn't seem to be available, and we shouldn't
let that prevent us from merging dbus changes. This can be reverted
when the runner comes back.

Signed-off-by: Simon McVittie <smcv@collabora.com>

.gitlab-ci.yml

@@ -50,6 +50,7 @@ variables:
 
 windows amd64 docker:
   stage: "build docker"
+  when: manual
   variables:
     # this file needs to be relative to docker/windows/ subdir
     # as it makes life easier in the powershell script
@@ -158,6 +159,7 @@ xenial:
 
 .win-build:
   image: $WINDOWS_IMAGE
+  when: manual
   stage: build
   tags:
     - 'docker'