This was an issue anymore on backends that allows conflicts to be
ignored (Refs #19544) as long the provided values were coercible to the
expected type. However on the remaining backends that don't support
this feature, namely Oracle, this could still result in an
IntegrityError.
By attempting to coerce the provided values to the expected types in
Python beforehand we allow the existing value set intersection in
ManyRelatedManager._get_missing_target_ids to prevent the problematic
insertion attempts.
Thanks Baptiste Mispelon for triaging this old ticket against the
current state of the master branch.
379bf1a2d4