Add codestyle action

.github/FUNDING.yml

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+# These are supported funding model platforms
+
+github: [infection]
+open_collective: infection

.github/tests_checker.yml

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+comment: Thank you for contributing to Infection. We noticed you didn't add any tests. Could you please add them to make sure everything works as expected?
+fileExtensions: ['.php']

.github/workflows/cs.yaml

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+# yamllint disable rule:line-length
+# yamllint disable rule:braces
+
+name: Coding Standards
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+      - master
+
+jobs:
+  coding-standards:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        operating-system: [ ubuntu-latest ]
+        php-version: [ '8.1' ]
+        check: [ 'cs' ]
+
+    name: Coding Standards on PHP ${{ matrix.php-version }}
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-version }}
+          tools: composer:v2
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: composer-${{ runner.os }}-${{ matrix.php-version }}-${{ hashFiles('composer.*') }}
+          restore-keys: |
+            composer-${{ runner.os }}-${{ matrix.php-version }}-
+            composer-${{ runner.os }}-
+            composer-
+
+      - name: Install dependencies
+        run: |
+          composer install --no-interaction --no-progress --prefer-dist
+
+      - name: Run ${{ matrix.check }}
+        run: make ${{ matrix.check }}