citemplate: only build rust docker images in gst-ci repos

They are only used by the gst-rs repos which aren't using
this template anyway, so we don't need to have the jobs for the
rest of the pipelines.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-ci/-/merge_requests/418>

gitlab/ci_template.yml

@@ -382,6 +382,8 @@ windows amd64 docker:
   needs:
     - job: 'windows amd64 docker'
       artifacts: false
+  rules:
+    - if: '$CI_PROJECT_NAME == "gst-ci"'
   variables:
     GIT_STRATEGY: 'fetch'