Fix failing PHPStan issue

[peter279k]

Changed log

• Removing remote Docker image about PHPStan. Using the composer phpstan script instead.
• Adding tests folder to be analysed via customized composer phpstan script.
• Adding the returning void type hint to fix following PHPStan issue:

peterli@peterli-Virtual-Machine:~/cron-expression$ php ~/composer.phar phpstan -n
For additional security you should declare the allow-plugins config with a list of packages names that are allowed to run code. See https://getcomposer.org/allow-plugins
You have until July 2022 to add the setting. Composer will then switch the default behavior to disallow all plugins.
> ./vendor/bin/phpstan analyse -l max src tests
Note: Using configuration file /home/peterli/cron-expression/phpstan.neon.
 18/18 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%

 ------ --------------------------------------------------------------------
  Line   tests/Cron/CronExpressionTest.php
 ------ --------------------------------------------------------------------
  639    Method Cron\Tests\CronExpressionTest::testGetParts() has no return
         typehint specified.
 ------ --------------------------------------------------------------------

 [ERROR] Found 1 error

Script ./vendor/bin/phpstan analyse -l max src tests handling the phpstan event returned with error code 1
peterli@peterli-Virtual-Machine:~/cron-expression$

[dragonmantank]

Thanks!