add GitHub workflows

.github/dependabot.yml

@@ -0,0 +1,13 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+
+  # Maintain dependencies for GitHub Actions
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/crystal.yml

@@ -0,0 +1,30 @@
+name: Crystal CI
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '0 0 1 * *'
+
+jobs:
+  check_format:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Crystal
+        uses: crystal-lang/install-crystal@v1
+      - name: Check out repository code
+        uses: actions/checkout@v4
+      - name: Check format
+        run: crystal tool format --check
+
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install Crystal
+        uses: crystal-lang/install-crystal@v1
+      - name: Check out repository code
+        uses: actions/checkout@v4
+      - name: Install dependencies
+        run: shards install
+      - name: Run tests
+        run: crystal spec