resolve_foreign_keys() used all-or-nothing isinstance checks, so mixing
ForeignKey objects with tuples raised "foreign_keys= should be a list of
tuples" - a regression from 3.x, where ForeignKey was a namedtuple and
passed the tuple check. Each item is now normalized individually, which
also allows bare column-name strings in a mixed list.
Refs https://github.com/simonw/sqlite-utils/issues/769#issuecomment-4900034150
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>