Migrate tests to GitHub Actions

The 13:44 trigger was chosen simply to match when Travis has been
triggering: https://api.github.com/repos/whatwg/misc-server/statuses/f8fd9dd5001bc14b277a734a4267226b73534e4c

It's not important to match that, but there is not default, and chosing
UTC midnight would lead to a spike in CI usage if we all did that.

.github/workflows/test.yml

@@ -0,0 +1,26 @@
+name: Test
+on:
+  pull_request:
+    branches:
+    - master
+  push:
+    branches:
+    - master
+  schedule:
+  - cron: '44 13 * * *'
+jobs:
+  test:
+    name: Test
+    runs-on: ubuntu-20.04
+    defaults:
+      run:
+        working-directory: test
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: true
+    - uses: actions/setup-node@v1
+      with:
+        node-version: 14
+    - run: npm install
+    - run: npm test