gitlab-ci: switch trigger-issuebot to variables: for reliable runs

Hopefully fix the failing result on some triggers:
"No stages / jobs for this pipeline."

.gitlab-ci.yml

@@ -194,10 +194,8 @@ fdroid build:
 pages:
   image: registry.gitlab.com/fdroid/ci-images-client:latest
   only:
-    - triggers
-    - web
-  except:
-    - master@fdroid/fdroiddata
+    variables:
+      - $FROM_CI_MERGE_REQUEST_IID && $CI_PROJECT_PATH != "fdroid/fdroiddata" && $CI_COMMIT_BRANCH != "master"
   artifacts:
     paths:
       - metadata/