[`BLIP`] fix doctest (#21217)
* fix `blip` doctest
* Update src/transformers/models/blip/modeling_blip.py
Co-authored-by: NielsRogge <48327001+NielsRogge@users.noreply.github.com>
Co-authored-by: NielsRogge <48327001+NielsRogge@users.noreply.github.com>
