refactor: add workflow to test older php versions

.github/workflows/test_backwards.yml

@@ -0,0 +1,45 @@
+name: Run tests against older PHP versions
+
+on:
+  push:
+    branches:
+      - main
+      - develop
+  pull_request:
+    branches:
+      - main
+      - develop
+  workflow_dispatch:
+  workflow_call:
+
+jobs:
+  test_backwards:
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        php-version: ['8.2']
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php-version }}
+          extensions: composer
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
+
+      - name: Cache dependencies
+        uses: actions/cache@v4
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}
+
+      - name: Install dependencies
+        run: composer install --no-progress --no-interaction --prefer-dist
+
+      - name: Run tests
+        run: composer run-script test