MAL has a concept of "titles waiting for approval". These titles
cannot be added to user lists, but they do show up on the website and
crucially, in search results.
However, trying to add such an "unapproved" title will return a 400
error response with the error "invalid_content".
Previously, the awaitSuccess() call would mean the generic "HTTP 400"
toast would be shown. Now, a dedicated informative error message is
shown instead.
# Conflicts:
# CHANGELOG.md
MajorTanya
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