bump pytest version

[MauriceHendrix]

Description

bump up pytest version

Motivation and Context

Non-pinned tests are failing this fixes that

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Documentation checklist

• [ ] I have updated all documentation in the code where necessary.
• [ ] I have checked spelling in all (new) comments and documentation.
• [ ] I have added a note to RELEASE.md if relevant (new feature, breaking change, or notable bug fix).

n/a

Testing

• [x] Testing is done automatically and codecov shows test coverage
• [ ] This cannot be tested automatically

[codecov[bot]]

Codecov Report

Merging #305 into master will increase coverage by 0.00%. The diff coverage is 98.60%.

@@           Coverage Diff           @@
##           master     #305   +/-   ##
=======================================
  Coverage   98.60%   98.60%           
=======================================
  Files           6        7    +1     
  Lines        1361     1362    +1     
  Branches      299      299           
=======================================
+ Hits         1342     1343    +1     
  Misses          7        7           
  Partials       12       12           

Impacted Files	Coverage Δ
cellmlmanip/parser.py	97.39% <97.39%> (ø)
cellmlmanip/printer.py	98.02% <98.02%> (ø)
cellmlmanip/units.py	98.41% <98.41%> (ø)
cellmlmanip/model.py	99.78% <99.78%> (ø)
cellmlmanip/__init__.py	100.00% <100.00%> (ø)
cellmlmanip/main.py	100.00% <100.00%> (ø)
cellmlmanip/rdf.py	100.00% <100.00%> (ø)

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