chore: use pull_request_target for auto-labeler on fork PRs (#488)

fix: use pull_request_target for auto-labeler on fork PRs

When a PR is opened from a fork repository, the GITHUB_TOKEN in
pull_request events only has read permissions, preventing the
autolabeler from adding labels. Using pull_request_target runs
the workflow in the context of the base repository with write
permissions, which is safe since the autolabeler only reads PR
metadata and adds labels without checking out any code.

Fixes auto-labeler failing on PR #487 from a fork.

Author: shenxianpeng

.github/workflows/labeler.yml

@@ -1,8 +1,8 @@
 name: PR Auto-labeler
 
 on:
-  # pull_request event is required for auto-labeler
-  pull_request:
+  # pull_request_target event is required for auto-labeler on fork PRs
+  pull_request_target:
     types: [opened, reopened, synchronize]
 
 permissions: {}