Use pull_request_target again

Author: msimberg

.github/workflows/spelling.yaml

@@ -4,7 +4,7 @@ name: Check Spelling
 on:
   push:
     branches: ['main']
-  pull_request:
+  pull_request_target:
     branches: ['main']
     types: ['opened', 'reopened', 'synchronize']
   issue_comment: