Adjust PR handling workflow permissions

Any key not present in the permissions will be set to none so we
need contents:read even though that is the default.

https://github.blog/changelog/2021-04-20-github-actions-control-permissions-for-github_token/

.github/workflows/pr-handling.yaml

@@ -11,14 +11,24 @@ name: Assign PR to author and reviewers
 #       committed code should _NOT_ be touched in any case.
 
 "on":
-  pull_request_target:
-    types: [ opened, reopened, ready_for_review ]
+  pull_request:
+#  pull_request_target:
+#    types: [ opened, reopened, ready_for_review ]
+permissions:
+  actions: write
+  checks: write
+  contents: write
+  deployments: write
+  issues: write
+  packages: write
+  pull-requests: write
+  repository-projects: write
+  security-events: write
+  statuses: write
 
 jobs:
   assign-pr:
     name: Assign PR to author
-    permissions:
-      contents: write
     runs-on: ubuntu-latest
     steps:
       - uses: toshimaru/auto-author-assign@v2.1.0