Fix: Do not use deprecated --diff-format option

[localheinz]

This pull request

• stops using the deprecated --diff-format option when running friendsofphp/php-cs-fixer

[codecov]

Codecov Report

Merging #690 (3c8e346) into main (63bf4a5) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main     #690   +/-   ##
=========================================
  Coverage     98.48%   98.48%           
  Complexity      110      110           
=========================================
  Files            25       25           
  Lines           330      330           
=========================================
  Hits            325      325           
  Misses            5        5           

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