DOC: fix the matplotlib warning emitted during builing docs
DOC: fix the matplotlib warning emitted during builing docs

Reviewed in gh-13755
vigna/scipy,WarrenWeckesser/scipy,ilayn/scipy,endolith/scipy,matthew-brett/scipy,scipy/scipy,perimosocordiae/scipy,zerothi/scipy,matthew-brett/scipy,matthew-brett/scipy,e-q/scipy,ilayn/scipy,scipy/scipy,andyfaff/scipy,zerothi/scipy,scipy/scipy,vigna/scipy,e-q/scipy,tylerjereddy/scipy,endolith/scipy,e-q/scipy,endolith/scipy,mdhaber/scipy,tylerjereddy/scipy,tylerjereddy/scipy,andyfaff/scipy,Eric89GXL/scipy,mdhaber/scipy,mdhaber/scipy,andyfaff/scipy,grlee77/scipy,zerothi/scipy,grlee77/scipy,anntzer/scipy,perimosocordiae/scipy,matthew-brett/scipy,Eric89GXL/scipy,e-q/scipy,mdhaber/scipy,Stefan-Endres/scipy,WarrenWeckesser/scipy,endolith/scipy,vigna/scipy,rgommers/scipy,ilayn/scipy,scipy/scipy,perimosocordiae/scipy,zerothi/scipy,rgommers/scipy,scipy/scipy,andyfaff/scipy,andyfaff/scipy,Stefan-Endres/scipy,anntzer/scipy,anntzer/scipy,WarrenWeckesser/scipy,Eric89GXL/scipy,Eric89GXL/scipy,anntzer/scipy,WarrenWeckesser/scipy,Stefan-Endres/scipy,rgommers/scipy,rgommers/scipy,Stefan-Endres/scipy,tylerjereddy/scipy,Eric89GXL/scipy,zerothi/scipy,WarrenWeckesser/scipy,vigna/scipy,perimosocordiae/scipy,WarrenWeckesser/scipy,ilayn/scipy,mdhaber/scipy,ilayn/scipy,scipy/scipy,ilayn/scipy,zerothi/scipy,matthew-brett/scipy,endolith/scipy,mdhaber/scipy,grlee77/scipy,Eric89GXL/scipy,Stefan-Endres/scipy,vigna/scipy,Stefan-Endres/scipy,e-q/scipy,rgommers/scipy,anntzer/scipy,grlee77/scipy,tylerjereddy/scipy,endolith/scipy,anntzer/scipy,andyfaff/scipy,perimosocordiae/scipy,grlee77/scipy,perimosocordiae/scipy