Add a clang-format error to force workflow failure (microsoft#5757)

This change _should_ fix the permissions issues and allow the PR format
checker to post comments into PRs on failure. The comments should
include the first 50 lines of the diff that clang-format produces and an
error with a link to the full log.

Unfortunately this can't really be tested until it is merged. The
`pull_request_target` event only occurs once the action is in the target
branch.

Parts of this change have been tested separately, but they haven't all
been tested together.

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

@@ -1,39 +1,38 @@
 name: 'PR clang-format checker'
 on:
-  pull_request:
+  pull_request_target:
     types:
       - opened
       - edited
       - synchronize
       - reopened
-permissions:
-  contents: read
-  pull-requests: write
-  issues: write
 jobs:
   check-pr-formatting:
+    permissions:
+      contents: read
+      pull-requests: write
+      checks: write
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
         with:
           fetch-depth: 0
       - name: install clang-format
         run: sudo apt install -y clang-format
-      - name: Comparing ${{ env.GITHUB_BASE_REF }} vs HEAD
+      - name: Comparing PR against target branch
+        env:
+          PR_NUMBER: ${{ github.event.number }}
+          GH_TOKEN: ${{ github.token }}
         run: |
             echo Comparing $GITHUB_BASE_REF vs HEAD
             git diff -U0 --no-color origin/$GITHUB_BASE_REF..HEAD | clang-format-diff -p1 | tee format.diff
             if [ -s "format.diff" ]
-            then 
+            then
+              echo PR contains clang-format violations. First 50 lines of the diff: >> message.txt
+              echo ``` >> message.txt
+              cat format.diff | head -n 50 >> message.txt
+              echo ``` >> message.txt
+              echo See [action log]\(https://github.com/microsoft/DirectXShaderCompiler/actions/runs/$GITHUB_RUN_ID/job/$GITHUB_JOB\) for the full diff.  >> message.txt
+              gh pr comment $PR_NUMBER --body-file message.txt
               exit 1
             fi
-      - if: failure()
-        uses: actions/github-script@v6
-        with:
-          script: |
-            github.rest.issues.createComment({
-              issue_number: context.issue.number,
-              owner: context.repo.owner,
-              repo: context.repo.repo,
-              body: 'PR contains clang-format violations. See [action log](https://github.com/microsoft/DirectXShaderCompiler/actions/runs/${{ env.GITHUB_RUN_ID }}/job/${{ env.GITHUB_JOB }}) for the full diff.'
-            })