workflow: only build doc on upstream

Author: Morg42

.github/workflows/builddevdoc.yml

@@ -8,6 +8,9 @@ on:
 
 jobs:
   build:
+    # Only run on the upstream repository — forks have no dev_doc companion repo
+    # and lack the PAT_TOKEN secret required for the deploy step.
+    if: github.repository == 'smarthomeNG/plugins'
     runs-on: ubuntu-22.04 #latest
     strategy:
       fail-fast: false