test: add _curationTaxPercentage 0 case

[fabian416]

This Pull Request adds a test case to ensure that the subgraph upgrade does not revert when _curationTaxPercentage is set to 0.

Resolves #891

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (eb4a03e) 92.69% compared to head (f71110d) 92.69%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #931   +/-   ##
=======================================
  Coverage   92.69%   92.69%           
=======================================
  Files          46       46           
  Lines        2369     2369           
  Branches      426      426           
=======================================
  Hits         2196     2196           
  Misses        173      173           

Flag	Coverage Δ
unittests	92.69% <ø> (ø)

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[pcarranzav]

LGTM, thank you!