ci: add Github Actions workflow to run checks

.github/workflows/validate.yml

@@ -0,0 +1,20 @@
+name: validate
+on: [push]
+
+jobs:
+  check:
+    runs-on: ubuntu:latest
+    strategy:
+      matrix:
+        environment: ["staging", "firefoxci"]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+          cache: pip
+      - name: Install dependencies
+        run: pip install -r requirements/test.txt
+      - name: Run checks
+        run: tc-admin check --environment ${{matrix.environment}}