Build releases only on tags or develop

Needed so we could push documentation updates to master without
triggering a rebuild

.gitlab-ci.yml

@@ -148,7 +148,7 @@ amd64:
   # TODO: Replace with upstream image when 1.9.0 comes out
   image: rinpatch/elixir:1.9.0-rc.0
   only: &release-only
-  - master@pleroma/pleroma
+  - tags
   - develop@pleroma/pleroma
   artifacts: &release-artifacts
     name: "pleroma-$CI_COMMIT_REF_NAME-$CI_COMMIT_SHORT_SHA-$CI_JOB_NAME"