[12.x] Format the Queued Email Failures code

[AhmedAlaa4611]

Description

This PR utilizing the imported Illuminate\Queue\SerializesModels trait.

[shaedrich]

Assuming, the changed line is the only one, I'd recommend renaming the PR to "Remove unused import" (or alternatively, put this into the description if you should insist on the current title)

[browner12]

the import is not visible in the code example we see, but is more than likely present in any Mail class that someone generates. this is purely because we're seeing a truncated view, so I'd recommend leaving it in.