Fix PHP 8.4 deprecations

Problem/Motivation

There are a few issues with PHP 8.4, all of them related to the implicitly nullable parameter being deprecated now, requiring an explicit marking declaration.

Checking the code using PHPCompatibility code sniffer:

FILE: /var/www/html/web/modules/contrib/storybook/src/Asset/UnoptimizedAssetResolver.php
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FOUND 0 ERRORS AND 2 WARNINGS AFFECTING 2 LINES
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 49 | WARNING | Implicitly marking a parameter as nullable is deprecated since PHP 8.4. Update the type to be explicitly nullable instead. Found implicitly nullable parameter: $language.
 60 | WARNING | Implicitly marking a parameter as nullable is deprecated since PHP 8.4. Update the type to be explicitly nullable instead. Found implicitly nullable parameter: $language.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------


FILE: /var/www/html/web/modules/contrib/storybook/src/PathProcessor/AbsolutePathProcessor.php
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
FOUND 0 ERRORS AND 2 WARNINGS AFFECTING 1 LINE
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 18 | WARNING | Implicitly marking a parameter as nullable is deprecated since PHP 8.4. Update the type to be explicitly nullable instead. Found implicitly nullable parameter: $request.
 18 | WARNING | Implicitly marking a parameter as nullable is deprecated since PHP 8.4. Update the type to be explicitly nullable instead. Found implicitly nullable parameter:
    |         | $bubbleable_metadata.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Time: 82ms; Memory: 6MB

exit status 1

Steps to reproduce

Test the code base with PHPCompatibility code sniffer.

Proposed resolution

Fix deprecations.

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

None.