CI: upgrade pip in benchmarks CI run
CI: upgrade pip in benchmarks CI run

A merge to master CI run just failed with:

  Could not find a version that satisfies the requirement
  pluggy<1.0.0a1,>=0.12 (from pytest) (from versions: )

  No matching distribution found for pluggy<1.0.0a1,>=0.12 (from pytest)
  You are using pip version 10.0.1, however version 21.1.2 is available.

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