setattr should happen only if ConcurentUpdate is not raised

[YasenKalinin]

in Versioned Mixin:
If versioned model instance is in transaction atomic(): and if setattr( instance, version_field, new_version) happens and ConcurrentUpdate is raised, python object is changed, but db is reverted. So: setattr should happen only if not raising ConcurrentUpdate
Maybe:
`

    to_change = {}
    for i, value_tuple in enumerate(values):
        if isinstance(value_tuple[0], VersionField):
            assert old_version == value_tuple[2]
            values[i] = (
                value_tuple[0],
                value_tuple[1],
                value_tuple[2] + 1,
            )
            to_change[ version_field.attname] = old_version + 1
            #setattr(self, version_field.attname, old_version + 1)

    updated = super(VersionedMixin, self)._do_update(
        base_qs=base_qs.filter(**{version_field.attname: old_version}),
        using=using,
        pk_val=pk_val,
        values=values,
        update_fields=update_fields if values else None,  # Make sure base_qs is always checked
        forced_update=forced_update
    )

    if not updated and base_qs.filter(pk=pk_val).exists():
        raise ConcurrentUpdate
    
    for vf_attname, new_version in to_change.items():
        setattr( self, vf_attname, new_version)
    
    return updated

`