Make registry mirror vars available to milestone and RC releases

Author: wilkinsona

Diff for: ci/pipeline.yml

@@ -365,6 +365,8 @@ jobs:
       RELEASE_TYPE: M
       GITHUB_USERNAME: ((github-username))
       GITHUB_TOKEN: ((github-ci-release-token))
+    vars:
+      <<: *registry-mirror-vars
   - put: github-pre-release
     params:
       name: generated-changelog/tag
@@ -394,6 +396,8 @@ jobs:
       RELEASE_TYPE: RC
       GITHUB_USERNAME: ((github-username))
       GITHUB_TOKEN: ((github-ci-release-token))
+    vars:
+      <<: *registry-mirror-vars
   - put: github-pre-release
     params:
       name: generated-changelog/tag