Update unit tests for latest codeception

.github/workflows/ci.yml

@@ -28,16 +28,18 @@ jobs:
     - name: PHP Lint
       run: if find . -name "*.php" ! -path "./vendor/*" -print0 | xargs -0 -n 1 -P 8 php -l | grep -v "No syntax errors detected"; then exit 1; fi
     
-    - name: Download codeception
-      if: matrix.php != '8.0'
-      run: wget https://codeception.com/releases/2.3.9/codecept.phar
+    - name: Download codeception (PHP 7.2 and above)
+      if: matrix.php >= '7.2'
+      run: wget https://codeception.com/codecept.phar
+    
+    - name: Download codeception (PHP 7.1 and below)
+      if: matrix.php <= '7.1'
+      run: wget https://codeception.com/php56/codecept.phar
     
     - name: Run PHP development server
-      if: matrix.php != '8.0'
       run: php -S localhost:8000 &
     
     - name: Build and run codeception
-      if: matrix.php != '8.0'
       run: |
         php codecept.phar build
         php codecept.phar run --debug --fail-fast --env travis