refactor: fix tests after smarter getPrivateMethodInvoker() return

[paulbalandan]

Description
Fixes the following phpstan errors after having smarter return type for getPrivateMethodInvoker().

------ ------------------------------------ 
  Line   tests/system/ControllerTest.php     
 ------ ------------------------------------ 
  :98    Result of closure (void) is used.   
         🪪  callable.void                   
         ✏️  tests/system/ControllerTest.php  
 ------ ------------------------------------ 

 ------ ------------------------------------------------------- 
  Line   tests/system/Database/ConfigTest.php                   
 ------ ------------------------------------------------------- 
  :171   Unreachable statement - code above always terminates.  
         🪪  deadCode.unreachable                               
         ✏️  tests/system/Database/ConfigTest.php               
  :211   Unreachable statement - code above always terminates.  
         🪪  deadCode.unreachable                               
         ✏️  tests/system/Database/ConfigTest.php               
 ------ ------------------------------------------------------- 

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

Okay, now I get it, I commented about it in the different PR - all is good.