ci: add workflow to check for missing migrations

.github/workflows/check-missing-migrations.yml

@@ -0,0 +1,24 @@
+name: Check for missing migrations
+
+on:
+  pull_request:
+jobs:
+  run-check:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install OS dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install libldap2-dev libsasl2-dev libssl-dev gettext poppler-utils poppler-data libpoppler-cpp-dev
+      - uses: actions/checkout@v2
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.9
+      - name: Install Dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+      - name: Check for missing migrations
+        run: |
+          python manage.py makemigrations --check --dry-run