fix a doctest error in src/sage/interfaces/polymake.py

[cxzhong]

Fixes #40461, Fixes an doctest error in polymake.py

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

#40461

[cxzhong]

Now It passed the tests

./sage -t --warn-long 5.0 --random-seed=233797780117811162927400537850871848271 src/sage/interfaces/polymake.py
Running doctests with ID 2025-07-21-14-45-14-696aab3b.
Git branch: develop
Git ref: 10.7.beta8-dirty
Running with SAGE_LOCAL='/home/zhongcx/sage/local' and SAGE_VENV='/home/zhongcx/sage/local/var/lib/sage/venv-python3.13'
Using --optional=4ti2,debian,e_antic,fricas,giac,jupymake,latte_int,lidia,msolve,normaliz,pip,sage,sage_spkg
Features to be detected: 4ti2,SAGE_SRC,benzene,bliss,buckygen,conway_polynomials,coxeter3,csdp,cvxopt,cvxopt,database_cremona_ellcurve,database_cremona_mini_ellcurve,database_cubic_hecke,database_ellcurves,database_graphs,database_jones_numfield,database_knotinfo,dot2tex,dvipng,ecm,flatter,fpylll,fricas,gap_package_atlasrep,gap_package_design,gap_package_grape,gap_package_guava,gap_package_hap,gap_package_polenta,gap_package_polycyclic,gap_package_qpa,gap_package_quagroup,gfan,giac,glucose,graphviz,imagemagick,info,ipython,jmol,jupymake,jupyter_sphinx,kenzo,kissat,latte_int,lrcalc_python,lrslib,mathics,matroid_database,mcqd,meataxe,meson_editable,mpmath,msolve,nauty,networkx,numpy,palp,pandoc,pdf2svg,pdftocairo,pexpect,phitigra,pillow,plantri,polytopes_db,polytopes_db_4d,pplpy,primecountpy,ptyprocess,pycosat,pycryptosat,pynormaliz,pyparsing,python_igraph,requests,rpy2,rubiks,sage.combinat,sage.geometry.polyhedron,sage.graphs,sage.groups,sage.libs.braiding,sage.libs.ecl,sage.libs.flint,sage.libs.gap,sage.libs.giac,sage.libs.homfly,sage.libs.linbox,sage.libs.m4ri,sage.libs.ntl,sage.libs.pari,sage.libs.singular,sage.misc.cython,sage.modular,sage.modules,sage.numerical.mip,sage.plot,sage.rings.complex_double,sage.rings.finite_rings,sage.rings.function_field,sage.rings.number_field,sage.rings.padics,sage.rings.polynomial.pbori,sage.rings.real_double,sage.rings.real_mpfr,sage.sat,sage.schemes,sage.symbolic,sage_numerical_backends_coin,sagemath_doc_html,scipy,singular,sirocco,sloane_database,sphinx,symengine_py,sympy,tdlib,threejs,topcom
Doctesting 1 file.
sage -t --warn-long 5.0 --random-seed=233797780117811162927400537850871848271 src/sage/interfaces/polymake.py
    [258 tests, 2.11s wall]
----------------------------------------------------------------------
All tests passed!
----------------------------------------------------------------------
Total time for all tests: 2.1 seconds
    cpu time: 1.7 seconds
    cumulative wall time: 2.1 seconds
Features detected for doctesting:

[fchapoton]

ok, maybe