[PHP 8.4] Fixes for implicit nullability deprecation

[Ayesh]

Fixes all issues that emit deprecation notices on PHP 8.4 for implicit nullable parameter type declarations.

See:

• RFC
• PHP 8.4: Implicitly nullable parameter declarations deprecated

Exclude potential changes in the Requests library and sodium_compat.

Trac ticket: https://core.trac.wordpress.org/ticket/60786

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[SergeyBiryukov]

Thanks for the PR! Merged in r58009.