[13.x] Restore missing model deletion for broadcast events

[Faiyajz]

When a queued broadcast event does not explicitly configure missing-model behavior, BroadcastEvent replaces its default $deleteWhenMissingModels value of true with null.

The queue payload consequently records deleteWhenMissingModels as false. If an Eloquent model serialized with the event is deleted before the queue worker processes it, the broadcast job fails with a ModelNotFoundException instead of being quietly discarded.

This PR preserves the existing true default when the underlying event does not provide a value.

Events that explicitly set $deleteWhenMissingModels to false continue to opt out of this behavior.

Regression tests have been added for both the default behavior and the explicit opt-out.

[jackbayliss]

could be a B/C no?

This defaults to false mostly looking at examples like the below

framework/src/Illuminate/Queue/Queue.php

Line 184 in bd6b543

'deleteWhenMissingModels' => $this->getAttributeValue($job, DeleteWhenMissingModels::class, 'deleteWhenMissingModels') ?? false,

[Faiyajz]

Thanks for pointing this out. Generic queued jobs do default to false. However, BroadcastEvent appears intentionally different: Taylor changed its $deleteWhenMissingModels property to default to true in commit a21ad160, titled “delete broadcast events that are missing models by default.”

A later forward merge introduced the constructor assignment that replaces this class-specific default with null. This PR restores that intended default while preserving an explicit $deleteWhenMissingModels = false, which is also covered by the regression test.