BUG: Add permissions to apply clang format action

Attempt to enable the pull request clang format action to work on forked pull
requests.

Background:

- actions/labeler#12
- https://github.blog/changelog/2021-04-20-github-actions-control-permissions-for-github_token/

.github/workflows/apply-clang-format.yml

@@ -1,15 +1,17 @@
 name: Apply clang-format to PR
 
 on:
-  pull_request:
+  pull_request_target:
     types: [labeled]
 
 jobs:
   clang-format:
     runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
       with:
          fetch-depth: 0
     - uses: InsightSoftwareConsortium/ITKApplyClangFormatAction@master