[Mainsite] updating a title's main cover in place causes version error

[Valle_reading_manga]

When replacing the main cover of a title, that is, deleting the previous version and uploading a new one instead, you get hit with an optimistic lock [...] version error.
This probably happens because replacing the main cover triggers a chain similar to the following:

1. Deleting the old cover causes the main cover for the series to be updated
2. Meanwhile, the new cover gets uploaded and processed
3. Adding the "new" main cover now triggers an error: optimistic lock, due to 1.

The covers still get updated just fine, but if you updated additional metadata alongside them, those changes won't be applied and inputs will have to be done again.

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As for why I think this isn't just some obscure edge case: Covers are typically featured in announcements or teasers prior to the release, but often those are at a smaller resolution, so they can be replaced with a better version after the release. Currently, due to the issue described above, doing so requires editing the title twice (to upload and delete the covers separately), if you don't want to get an error. This is especially true for initial volumes, where you might want to update metadata like retail links alongside the cover.

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Thanks to @Bartolumiu for helping me figure this one out (probably?)