PHP 8.4 compatibility (dependency to localheinz/diff causes issue)

[simonschaufi]

Steps required to reproduce the problem

1. Run composer normalize under PHP 8.4

Expected Result

• No deprecation warnings

Actual Result

Deprecation Notice: Localheinz\Diff\Differ::diff(): Implicitly marking parameter $lcs as nullable is deprecated, the explicit nullable type must be used instead in /vendor/localheinz/diff/src/Differ.php:85
Deprecation Notice: Localheinz\Diff\Differ::diffToArray(): Implicitly marking parameter $lcs as nullable is deprecated, the explicit nullable type must be used instead in /vendor/localheinz/diff/src/Differ.php:111