add .github workflow

.gitattributes

@@ -1,6 +1,7 @@
 tests/                  export-ignore
 .gitattributes          export-ignore
 .gitignore              export-ignore
+.github                 export-ignore
 composer.*              export-ignore
 phpunit.*               export-ignore
 phpstan.neon            export-ignore

.github/workflows/main.yml

@@ -0,0 +1,73 @@
+# This is a basic workflow to help you get started with Actions
+
+name: CI
+
+# Controls when the action will run.
+on:
+  # Triggers the workflow on push or pull request events
+  push:
+  pull_request:
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # Composer config validation
+  composer:
+    name: "Composer config validation"
+    runs-on: "ubuntu-latest"
+    steps:
+      - uses: "actions/checkout@v3"
+      - name: "Validate composer.json"
+        run: "composer validate --strict"
+
+  # PHP syntax validation
+  php:
+    name: "PHP syntax validation"
+    runs-on: "ubuntu-latest"
+    strategy:
+      matrix:
+        php_version: [ 8.1, 8.2, 8.3 ]
+    steps:
+      - uses: "actions/checkout@v3"
+      - uses: "shivammathur/setup-php@v2"
+        with:
+          php-version: "${{ matrix.php_version }}"
+
+      - name: "Check PHP syntax of package"
+        run: |
+          php -l src/
+          php -l tests/
+
+  phpunit:
+    name: "PHPUnit tests"
+    runs-on: "ubuntu-latest"
+    strategy:
+      matrix:
+        php_version: [ 8.1, 8.2, 8.3 ]
+    steps:
+      - uses: "actions/checkout@v3"
+      - uses: "php-actions/composer@v6"
+        with:
+          php_version: "${{ matrix.php_version }}"
+          php_extensions: intl
+      - run: "vendor/bin/phpunit"
+
+  # phpstan for several php versions
+  phpstan:
+    runs-on: "ubuntu-latest"
+    strategy:
+      matrix:
+        php_version: [ 8.1, 8.2, 8.3 ]
+    steps:
+      - uses: "actions/checkout@v3"
+      - uses: "php-actions/composer@v6"
+        with:
+          php_version: "${{ matrix.php_version }}"
+          php_extensions: intl
+      - name: "PHPStan Static Analysis"
+        uses: "php-actions/phpstan@v3"
+        with:
+          php_version: "${{ matrix.php_version }}"
+          configuration: "phpstan.neon"