Fixing PHPStan level 4 issues

Author: gplanchat

.github/workflows/quality.yaml

@@ -1,4 +1,4 @@
-name: Quality (PHPStan level 3)
+name: Quality (PHPStan level 4)
 on: push
 jobs:
   cs-fixer:

README.md

@@ -5,7 +5,7 @@ This package brings an implementation for the pipeline component, aimed at provi
 with logging, line rejections and execution states.
 
 
-[![Quality](https://github.com/php-etl/pipeline/actions/workflows/quality.yaml/badge.svg)](https://github.com/php-etl/pipeline/actions/workflows/quality.yaml)
+[![Quality (PHPStan level 4)](https://github.com/php-etl/pipeline/actions/workflows/quality.yaml/badge.svg)](https://github.com/php-etl/pipeline/actions/workflows/quality.yaml)
 [![PHPUnit](https://github.com/php-etl/pipeline/actions/workflows/phpunit.yaml/badge.svg)](https://github.com/php-etl/pipeline/actions/workflows/phpunit.yaml)
 [![Mutations](https://github.com/php-etl/pipeline/actions/workflows/infection.yaml/badge.svg)](https://github.com/php-etl/pipeline/actions/workflows/infection.yaml)
 [![PHPStan level 5](https://github.com/php-etl/pipeline/actions/workflows/phpstan-5.yaml/badge.svg)](https://github.com/php-etl/pipeline/actions/workflows/phpstan-5.yaml)