CI: fix testing of `SCIPY_USE_PYTHRAN=0`, and upgrade to pythran 0.12.0
CI: fix testing of `SCIPY_USE_PYTHRAN=0`, and upgrade to pythran 0.12.0

xref gh-17102, which discovered that the `=0` usage is currently broken.

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andyfaff/scipy,endolith/scipy,scipy/scipy,Stefan-Endres/scipy,scipy/scipy,endolith/scipy,WarrenWeckesser/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,andyfaff/scipy,andyfaff/scipy,anntzer/scipy,mdhaber/scipy,andyfaff/scipy,andyfaff/scipy,ilayn/scipy,mdhaber/scipy,endolith/scipy,scipy/scipy,WarrenWeckesser/scipy,WarrenWeckesser/scipy,ilayn/scipy,mdhaber/scipy,endolith/scipy,anntzer/scipy,scipy/scipy,ilayn/scipy,scipy/scipy,endolith/scipy,mdhaber/scipy,anntzer/scipy,mdhaber/scipy,ilayn/scipy,WarrenWeckesser/scipy,anntzer/scipy,WarrenWeckesser/scipy,mdhaber/scipy,ilayn/scipy,anntzer/scipy,WarrenWeckesser/scipy,endolith/scipy,anntzer/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,ilayn/scipy,andyfaff/scipy,scipy/scipy