change trigger for spellchecker

Author: msimberg

.github/workflows/spelling.yaml

@@ -2,13 +2,8 @@ name: Check Spelling
 
 # Based on example in https://github.com/check-spelling/spell-check-this.
 on:
-  pull_request_target:
-    branches:
-    - "**"
-    types:
-    - 'opened'
-    - 'reopened'
-    - 'synchronize'
+  pull_request:
+    branches: ['main']
   issue_comment:
     types:
     - 'created'