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.

I see the issue #3505552: Deprecated: Implicitly nullable in PHP 8.4 fixed a few, but a couple still remains, most specifically for the Context UI submodule.

Checking the code using PHPCompatibility code sniffer:

FILE: /var/www/html/web/modules/contrib/context/modules/context_ui/src/Form/ConditionDeleteForm.php
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FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
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 92 | 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: $context.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------


FILE: /var/www/html/web/modules/contrib/context/modules/context_ui/src/Form/ReactionDeleteForm.php
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 95 | 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: $context.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Time: 351ms; Memory: 8MB

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.