Added migration label to PRs containing migrations

- this helps us to filter PRs for migrations in the future

.github/workflows/migration-review.yml

@@ -9,8 +9,18 @@ jobs:
   createComment:
     runs-on: ubuntu-latest
     if: github.repository_owner == 'TryGhost'
-    name: Create checklist comment
+    name: Add migration review requirements
     steps:
+      - uses: actions/github-script@v6
+        with:
+          script: |
+            github.rest.issues.addLabels({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              labels: ["migration"]
+            })
+
       - uses: peter-evans/create-or-update-comment@e0e8aa00752bbac08c4393c1f7834e6ee753c159
         with:
           issue-number: ${{ github.event.pull_request.number }}