Migrate CI from Travis to Github Actions

.github/workflows/tests.yaml

@@ -0,0 +1,50 @@
+name: CI
+
+on:
+  pull_request: ~
+  push:
+    branches:
+      - master
+  schedule:
+    - cron: "47 6 * * 1" # once a month, to surface issues with newer dependencies
+
+jobs:
+  Tests:
+    runs-on: 'ubuntu-latest'
+    strategy:
+      matrix:
+        php:
+          - '7.4'
+          - '8.0'
+          - '8.1'
+          - '8.2'
+          - '8.3'
+          - '8.4'
+        dependencies: ['highest']
+        include:
+          - description: '(lowest)'
+            php: '7.4'
+            dependencies: 'lowest'
+
+    name: PHP ${{ matrix.php }} ${{ matrix.description }}
+    steps:
+      - name: "Checkout"
+        uses: actions/checkout@v4
+      - name: "Install PHP"
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          coverage: xdebug
+      - name: "Install dependencies"
+        uses: ramsey/composer-install@v3
+        with:
+          dependency-versions: ${{ matrix.dependencies }}
+      - name: "Run PHPStan analysis"
+        run: composer phpstan
+      - name: "Run tests"
+        run: vendor/bin/phpunit --coverage-clover=coverage.xml --colors=always
+      - name: "Upload test coverage"
+        uses: codecov/codecov-action@v5
+        with:
+          files: './coverage.xml'
+          fail_ci_if_error: true