MAINT: fix type-narrowing addition in sparse.construct.bmat (#14626)
MAINT: fix type-narrowing addition in sparse.construct.bmat (#14626)

Closes gh-14623

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