ci: add .github/workflows/tests.yml

This runs against rakudo-star:latest for now. We'll need to find
a way to test against a list of recent versions to detect regressions.

.github/workflows/tests.yml

@@ -0,0 +1,22 @@
+name: Run test script
+
+on:
+  push:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  test-script:
+    runs-on: ubuntu-latest
+
+    container:
+      image: rakudo-star:latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Run Test Script
+        run: sh ./bin/test-script.sh
+