Add a Github Action to ensure the CHANGELOG is updated in PRs

.github/workflows/check-updated-changelog.yml

@@ -0,0 +1,15 @@
+name: Check if the CHANGELOG.md has been updated
+
+on: [pull_request]
+
+jobs:
+  check:
+    name: Test on ${{ matrix.os }}
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Checking the CHANGELOG.md has been updated in this PR
+      run: |
+        set -e
+        git fetch origin ${{ github.base_ref }}
+        git diff --name-only origin/${{ github.base_ref }} | grep -q CHANGELOG.md