[9.x] Have Model::withoutTimestamps() return the callback's return value

[axlon]

#44138 introduced the ability to perform actions on models without timestamps.

This PR makes Model::withoutTimestamps() act the same as Model::withoutEvents(), Model::withoutTimestampsOn() and various other "without" methods, by having it return the callbacks return value.

This would then allow e.g.:

$user = User::withoutTimestamps(fn () => User::create($request->validated());

[internetbuilder]

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