Make beam_constraints.Constraint.advance() docstring more accurate (#32674)
* Fix beam_constraints.Constraint.advance() docstring
* Update src/transformers/generation/beam_constraints.py
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>
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Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>