Env-specific tests fail depending on random execution order

[Ocramius]

Bug Report

Q	A
Version(s)	1.20.0

#220 introduced new environment variables, but the tests around it fail due to missing isolation of global state during test execution.

See for example #223 failure @ https://github.com/laminas/automatic-releases/actions/runs/3716382625/jobs/6302643279#step:3:512

Error: ] Project tests must be in a passing state before running Infection.     
         Infection runs the test suite in a RANDOM order. Make sure your tests  
         do not have hidden dependencies.                                       
                                                                                
         You can add these attributes to `phpunit.xml` to check it: <phpunit    
         executionOrder="random" resolveDependencies="true" ...                 
                                                                                
         If you don't want to let Infection run tests in a random order, set the
         `executionOrder` to some value, for example <phpunit                   
         executionOrder="default"                                               
                                                                                
         Check the executed command to identify the problem:                    
         '/usr/bin/phpdbg8.1' '-qrr' '/github/workspace/vendor/bin/phpunit'     
         '--configuration'                                                      
         '/tmp/infection/phpunitConfiguration.initial.infection.xml'            
         '--coverage-xml=/tmp/infection/coverage-xml'                           
         '--log-junit=/tmp/infection/junit.xml'                                 
         PHPUnit reported an exit code of 1.                                    
         Refer to the PHPUnit's output below:                                   
         STDOUT:                                                                
         PHPUnit 9.5.27 by Sebastian Bergmann and contributors.                 
                                                                                
         Runtime:       PHPDBG 8.1.13                                           
         Configuration:                                                         
         /tmp/infection/phpunitConfiguration.initial.infection.xml              
         Random Seed:   1671223208                                              
                                                                                
         ...............................................................  63 /  
         229 ( 27%)                                                             
         ........................F                                              
                                                                                
         Time: 00:02.168, Memory: 46.00 MB                                      
                                                                                
         There was 1 failure:                                                   
                                                                                
         1)                                                                     
         Laminas\AutomaticReleases\Test\Unit\Environment\EnvironmentVariablesTes
         t::testDebugModeOffEnvironmentVariables                                
         Failed asserting that two strings are equal.                           
         --- Expected                                                           
         +++ Actual                                                             
         @@ @@                                                                  
         -'INFO'                                                                
         +'DEBUG'                                                               
                                                                                
         /github/workspace/test/unit/Environment/EnvironmentVariablesTest.php:13
         1                                                                      
                                                                                
         FAILURES!                                                              
         Tests: 88, Assertions: 296, Failures: 1.                               
                                                                                
         Generating code coverage report in PHPUnit XML format ... done         
         [00:00.288]                                                            \

Should be reproducible with the same random seed.

[Ocramius]

Handled in #225