Add workflow to request Copilot review on maintainer PRs (#1587) (#1588)

Fires on pull_request_target (opened, reopened, ready_for_review) and
only requests review when author_association is OWNER, MEMBER, or
COLLABORATOR. Drafts are skipped. Uses pull_request_target so the job
has write access on fork-based PRs.

Author: brendancol

.github/workflows/copilot-review.yml

@@ -0,0 +1,27 @@
+name: Request Copilot review
+
+on:
+  pull_request_target:
+    types: [opened, reopened, ready_for_review]
+
+permissions:
+  pull-requests: write
+
+jobs:
+  request-copilot-review:
+    if: >-
+      github.event.pull_request.draft == false &&
+      contains(fromJSON('["OWNER", "MEMBER", "COLLABORATOR"]'), github.event.pull_request.author_association)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Request Copilot review
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
+          REPO: ${{ github.repository }}
+        run: |
+          gh api \
+            --method POST \
+            -H "Accept: application/vnd.github+json" \
+            "/repos/${REPO}/pulls/${PR_NUMBER}/requested_reviewers" \
+            -f "reviewers[]=Copilot"