Run tests in CI

Not running the BrowserStack ones because I don’t want to spend time
getting credentials set up right now.

I’ve changed the browser to headless to avoid the error "no DISPLAY
environment variable specified" in CI.

.github/workflows/check.yaml

@@ -0,0 +1,27 @@
+name: Check
+on:
+  workflow_dispatch:
+  pull_request:
+  push:
+    branches:
+      - main
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Use Python 3.8
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.8'
+
+      - name: Use Node.js 8.x
+        uses: actions/setup-node@v4
+        with:
+          node-version: 8.x
+
+      - run: npm ci
+      - run: npm run grunt -- test:node
+      - run: npm run grunt -- test:browser:local

Gruntfile.js

@@ -124,7 +124,7 @@ module.exports = function (grunt) {
 			},
 			local: {
 				reporters: ['progress', 'mocha'],
-				browsers: ['Firefox'],
+				browsers: ['FirefoxHeadless'],
 			},
 			remote: {
 				browserStack: {