Add code checks CI job

.github/workflows/checks.yml

@@ -0,0 +1,23 @@
+name: checks
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
+        with:
+          node-version: 16
+          cache: yarn
+      - run: yarn install --frozen-lockfile
+      - run: yarn check:types
+      - run: yarn check:style

.prettierignore

@@ -0,0 +1 @@
+*.d.ts

package.json

@@ -12,7 +12,8 @@
     "test": "jest",
     "test:server": "jest server/tests",
     "test:ci": "jest --runInBand",
-    "check:types": "tsc --noEmit -p server/tsconfig.json"
+    "check:types": "tsc --noEmit -p server/tsconfig.json",
+    "check:style": "prettier --check **/*.ts"
   },
   "devDependencies": {
     "@types/jest": "27.0.1",