Symfony 7 support

[IonBazan]

As Symfony 7 adds return types to Commands which is a breaking change. To mitigate this, I did some hacks in order to maintain compatibility with both PHP 5.3 and older versions of Symfony by adding two base command variants and a conditional alias 🤮

Note: This only affects people using this library as a binary (vendor/bin/composer-diff) in a project where composer/composer and symfony/console are installed as dependencies. You can still use it as a Composer plugin (composer diff) with any version of Symfony without upgrading.

Doesn't look nice but works like a charm (see tests)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7482e1f) 100.00% compared to head (005967f) 100.00%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##                main       #29   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity       206       206           
===========================================
  Files             19        19           
  Lines            596       610   +14     
===========================================
+ Hits             596       610   +14     

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