MAINT: bump PYVER pavement.py
MAINT: bump PYVER pavement.py

* bump the version of `PYVER` in `pavement.py` so that it
is one of our currently supported versions for the
release process

* as discussed in the issue, this is not super important, I chose
`3.9` so that we hopefully don't have to change this again before
we stop using this infrastructure

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