ci: Fix pr-code-format permissions for private forks

The action requires the ability to change the contents of a pull request (by
adding the formatting-related comment) which is only possible through
the `write` permission, but if this permission is missing, potential
private forks with Actions enabled will break, and because the action
triggers on `pull_request_target` even a PR initially fixing this issue
downstream will not exhibit the fix until merged.

Author: whisperity

.github/workflows/pr-code-format.yml

@@ -2,6 +2,8 @@ name: "Check code formatting"
 
 permissions:
   contents: read
+  issues: write
+  pull-requests: write
 
 on:
   pull_request: