Bugfix WorkflowDefinitionUpsert storing built-in hash function

[haakonvt]

Description

Belongs in the subclass only, the READ version (and not hash, but "hash from API").

Also adds a test.

Checklist:

• Tests added/updated.
• Documentation updated. Documentation is generated from docstrings - these must be updated according to your change.
  If a new method has been added it should be referenced in cognite.rst in order to generate docs based on its docstring.
• Changelog updated in CHANGELOG.md.
• Version bumped. If triggering a new release is desired, bump the version number in _version.py and pyproject.toml per semantic versioning.

[codecov]

Codecov Report

Merging #1539 (443dd7b) into master (6529464) will increase coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1539      +/-   ##
==========================================
+ Coverage   91.75%   91.76%   +0.01%     
==========================================
  Files         120      120              
  Lines       15600    15599       -1     
==========================================
+ Hits        14313    14314       +1     
+ Misses       1287     1285       -2     

Files	Coverage Δ
cognite/client/_version.py	100.00% <100.00%> (ø)
cognite/client/data_classes/workflows.py	95.71% <ø> (-0.02%)	⬇️

... and 1 file with indirect coverage changes

[doctrino]

Nice