add workflow

Author: TomasVotruba

.editorconfig

@@ -0,0 +1,9 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4

.github/workflows/compat_tests.yaml.yml

@@ -0,0 +1,46 @@
+name: Compat Tests
+
+on:
+    pull_request: null
+    push:
+        branches:
+            - main
+
+jobs:
+    compat_tests:
+        strategy:
+            fail-fast: false
+            matrix:
+                actions:
+                    -
+                        name: 'Along PHPUnit 9'
+                        run: composer require "phpunit/phpunit:9.*"
+                    -
+                        name: 'Along PHPUnit 10'
+                        run: composer require "phpunit/phpunit:10.*"
+                    -
+                        name: 'Along PHPUnit 11'
+                        run: composer require "phpunit/phpunit:11.*"
+                    -
+                        name: 'Along PHPUnit 12'
+                        run: composer require "phpunit/phpunit:12.*"
+
+        name: ${{ matrix.actions.name }}
+
+        runs-on: ubuntu-latest
+
+        steps:
+            -   uses: actions/checkout@v4
+
+            -
+                uses: shivammathur/setup-php@v2
+                with:
+                    php-version: 8.2
+                    coverage: none
+
+            -   uses: "ramsey/composer-install@v2"
+
+            -   run: ${{ matrix.actions.run }}
+
+            # run all tests
+            -   run: vendor/bin/phpunit