Move from Travis to GitHub Actions

Author: danmichaelo

.github/workflows/main.yml

@@ -0,0 +1,22 @@
+name: CI
+
+on: [push]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php_version:
+          - 8.0
+          - 8.1
+    steps:
+    - uses: actions/checkout@v2
+    - uses: php-actions/composer@v6
+      with:
+        php_version: ${{ matrix.php_version }}
+    - uses: php-actions/phpunit@v3
+      with:
+        php_version: ${{ matrix.php_version }}
+        php_extensions: pcov
+    - run: bash <(curl -s https://codecov.io/bash)