Re: "lock file exists" when fetching in bare clone of repository

> This error type is bubbled up to `files_transaction_prepare()` which
> tries to lock each reference update by calling `lock_ref_for_update()`.
> So if the locking fails, we check if the rejection type can be ignored,
> which is done by calling `ref_transaction_maybe_set_rejected()`.
>
> Only during batched updates would errors be ignore and only for
> non-generic errors. So this change would specifically only apply for
> batched updates. Currently that is used by:
>
>     1. git fetch
>     2. git receive-pack
>     3. git update-ref --batch-updates
>
> And for all three scenarios I think it makes sense to add this in.