Ensure we have the latest pip version in build environments

[mochipon]

Ref. mochipon/pysesame3#30

[codecov]

Codecov Report

Merging #7 (ff33791) into main (58d711d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main       #7   +/-   ##
=======================================
  Coverage   95.63%   95.63%           
=======================================
  Files           7        7           
  Lines         824      824           
=======================================
  Hits          788      788           
  Misses         36       36           

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