ci: drop pull_request_target from PR checks workflow (llm-d#1326)

The dual-event registration was a workaround for PRs created with GITHUB_TOKEN, which do not fire pull_request. Both PR-creating workflows in this repo now use App-installation tokens, which do fire pull_request, so pull_request_target is redundant and only produces duplicate SKIPPED check rows on every PR.

Signed-off-by: Etai Lev Ran <elevran@gmail.com>

Author: elevran

.github/workflows/ci-pr-checks.yaml

@@ -8,10 +8,6 @@ on:
   pull_request:
     branches:
       - main
-  pull_request_target:
-    branches:
-      - main
-    types: [ opened, synchronize, reopened ]
 
 permissions:
   contents: read
@@ -23,12 +19,6 @@ concurrency:
 
 jobs:
   check-changes:
-    # pull_request_target fires even when GITHUB_TOKEN creates the PR (e.g. the
-    # release-notes bot). pull_request does not. We register pull_request_target
-    # so bot-created PRs get a "skipped" conclusion that satisfies branch
-    # protection, but we skip all real work: pull_request already covers human
-    # PRs, and running twice would cause the concurrency group to cancel one run.
-    if: github.event_name != 'pull_request_target'
     runs-on: ubuntu-latest
     outputs:
       src: ${{ steps.filter.outputs.src }}