CI: clean up jobs for PHP 7.4

Both tests and Fixer are run twice:
- on Symfony ^5 components with `--prefer-lowest` flag for Composer deps
- on highest deps available for this PHP version

Native type checks are run along with regular Fixer checks because they take only few seconds and there's no need to extract it to separate job - this wouldn't be optimisation.

.github/workflows/ci.yml

@@ -19,26 +19,29 @@ jobs:
         include:
           - operating-system: 'ubuntu-20.04'
             php-version: '7.4'
-            job-description: 'tests with Symfony ^5'
-            run-tests: 'yes'
+            job-description: 'Fixer with lowest deps'
+            run-fixer: 'yes'
+            run-phpdoc-to-native-type: 'yes' # should be checked on the lowest supported PHP version
+            composer-flags: '--prefer-lowest' # should be checked on the lowest supported PHP version
             execute-flex-with-symfony-version: '^5' # explicit check for Symfony 5.x compatibility
 
           - operating-system: 'ubuntu-20.04'
             php-version: '7.4'
-            job-description: 'Fixer with lowest deps'
+            job-description: 'tests with lowest deps'
             run-fixer: 'yes'
             composer-flags: '--prefer-lowest' # should be checked on the lowest supported PHP version
+            execute-flex-with-symfony-version: '^5' # explicit check for Symfony 5.x compatibility
 
           - operating-system: 'ubuntu-20.04'
             php-version: '7.4'
-            job-description: 'Fixer with PHPDoc to type rules'
+            job-description: 'Fixer'
+            run-fixer: 'yes'
             run-phpdoc-to-native-type: 'yes' # should be checked on the lowest supported PHP version
 
           - operating-system: 'ubuntu-20.04'
             php-version: '7.4'
-            job-description: 'Fixer with Symfony ^5'
-            run-fixer: 'yes'
-            execute-flex-with-symfony-version: '^5' # explicit check for Symfony 5.x compatibility
+            job-description: 'tests'
+            run-tests: 'yes'
 
           - operating-system: 'ubuntu-20.04'
             php-version: '8.0'