Update antora-build.yml

Only trigger generator if the PR has access to the required secrets.

Author: philipwindecker

.github/workflows/antora-build.yml

@@ -12,8 +12,12 @@ jobs:
 
     runs-on: Ubuntu-latest
 
+    env:
+      MUP_KEY: ${{ secrets.MACHINE_USER_PAT }}
+
     steps:
     - name: Trigger generator
+      if: ${{ env.MUP_KEY != '' }}
       uses: peter-evans/repository-dispatch@v2
       with:
         token: ${{ secrets.MACHINE_USER_PAT }}
@@ -66,4 +70,4 @@ jobs:
   #       name: antora-build
   #       path: ./generator/site
 
-      
+