DOC: BLD: improve doc buid time by turning off sidebar expansion in refguide
DOC: BLD: improve doc buid time by turning off sidebar expansion in refguide

Taken over from Pandas PR 40761, where it sped up doc build time by just
over 2x.

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