github: Fix checklist action

Workflows triggered by the 'pull_request' event can't have write
permissions. With write permissions a malicious pull request can alter
or create a workflow that either leaks the GITHUB_TOKEN with the write
permissions or do malicious things in the workflow itself.

The 'pull_request_target' event on the other hand allows workflows to
run with write permissions but runs on the merge base of the PR, this
way a pull request that alters such a workflow will not have it's code
run until it's merged.

Signed-off-by: Ahmad Khalifa <[email protected]>

.github/workflows/checklist.yml

@@ -4,7 +4,7 @@ name: Checklist
 # for the submission to align with CONTRIBUTING.md
 
 on:
-  pull_request:
+  pull_request_target:
     types: [ opened, reopened, edited, synchronize ]
 
 permissions: