Enhancement: Add support for PHP 7.4

[localheinz]

This pull request

• adds support for PHP 7.4

[codecov]

Codecov Report

Attention: Patch coverage is 10.00000% with 18 lines in your changes missing coverage. Please review.

Project coverage is 85.52%. Comparing base (3c69cb8) to head (47fcd1e).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Classes/FinalRule.php	0.00%	1 Missing ⚠️
src/Classes/NoExtendsRule.php	0.00%	1 Missing ⚠️
...asses/PHPUnit/Framework/TestCaseWithSuffixRule.php	0.00%	1 Missing ⚠️
...c/Closures/NoNullableReturnTypeDeclarationRule.php	0.00%	1 Missing ⚠️
...c/Closures/NoParameterWithNullDefaultValueRule.php	0.00%	1 Missing ⚠️
...res/NoParameterWithNullableTypeDeclarationRule.php	0.00%	1 Missing ⚠️
src/Expressions/NoCompactRule.php	0.00%	1 Missing ⚠️
src/Files/DeclareStrictTypesRule.php	0.00%	1 Missing ⚠️
.../Functions/NoNullableReturnTypeDeclarationRule.php	0.00%	1 Missing ⚠️
.../Functions/NoParameterWithNullDefaultValueRule.php	0.00%	1 Missing ⚠️
... and 8 more

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #880   +/-   ##
=========================================
  Coverage     85.52%   85.52%           
  Complexity      208      208           
=========================================
  Files            23       23           
  Lines           739      739           
=========================================
  Hits            632      632           
  Misses          107      107           

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