Update if-not-tag-fail.yaml

Author: mtintes

.github/workflows/if-not-tag-fail.yaml

@@ -6,6 +6,7 @@ on:
 jobs:
     job1:
         runs-on: ubuntu-latest
+        if: startsWith(github.ref, 'refs/tags/')        
         steps:
             - name: fail if main branch
               run: |