ci: check for changeset integrity (#2415)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

.github/workflows/changesets.yml

+---
+name: 'Changeset integrity checker'
+on:
+  - pull_request_target
+
+jobs:
+  changesets-integrity-checker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: 'changeset status'
+        run: npx changeset status