Move CI to GitHub Actions

Closes #725.
Closes #726.

Co-authored-by: Jean Boussier <jean.boussier@gmail.com>

.github/workflows/test.yml

@@ -0,0 +1,36 @@
+name: test
+
+on: [push, pull_request]
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+
+      matrix:
+        ruby-version:
+          - '2.3'
+          - '2.4'
+          - '2.5'
+          - '2.6'
+          - '2.7'
+          - '3.0'
+          - '3.1'
+          - '3.2'
+          - '3.3'
+          - ruby-head
+
+    steps:
+      - run: sudo apt-get install -y tidy tcl tk
+
+      - uses: actions/checkout@v3
+
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby-version }}
+          bundler-cache: true
+        continue-on-error: ${{ matrix.ruby-version == 'ruby-head' }}
+
+      - run: bundle exec rake
+        continue-on-error: ${{ matrix.ruby-version == 'ruby-head' }}