Run the test suite using GitHub Actions

Using GitHub Actions has a few advantages over using Travis CI:

* More jobs can be run in parallel
* All CONSUL repositories on GitHub will be configured automatically

Besides, Travis have recently changed their policy twice. First, they
announced their site for free software projects would be shut down but
free software projects could still use their site for private projects.
And then, they limited the usage of their services for free software
projects.

Just like we used to do with Travis, we're enabling builds for pull
requests but not for pushed branches.

We're also building the master branch. Even if we never push to the
master branch directly, we're aware other CONSUL repositories do, so
we're running the tests for this case.

.github/workflows/tests.yml

@@ -0,0 +1,40 @@
+name: Test suite
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches-ignore:
+      - i18n_master
+
+jobs:
+  test:
+    runs-on: ubuntu-18.04
+    services:
+      postgres:
+        image: postgres:10.10
+        ports: ["5432:5432"]
+        options: --health-cmd pg_isready --health-interval 10s --health-timeout 5s --health-retries 5
+        env:
+          POSTGRES_USER: consul
+          POSTGRES_PASSWORD: ""
+    env:
+      PGUSER: consul
+      POSTGRES_HOST: postgres
+      RAILS_ENV: test
+      COVERALLS: true
+    steps:
+      - uses: actions/checkout@v2
+      - uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+      - name: Setup NPM
+        uses: actions/setup-node@v1
+      - name: Copy secrets and database files
+        run: for i in config/*.example; do cp "$i" "${i/.example}"; done
+      - name: Setup database
+        run: bundle exec rake db:setup
+      - name: Compile assets
+        run: bundle exec rake assets:precompile > /dev/null 2>&1
+      - name: Run test suite
+        run: bin/rspec