patch: fix gridline tests for np 2.x

[bjlittle]

🚀 Pull Request

Description

Now that pyvista 0.44 is released with numpy 2.x support 🥳, it made it easy to investigate and propose the simple fix to address the failing geovista.gridlines tests.

Essentially, numpy 2.x was injecting the scalar type for the __repr__ used in the multi-blocks keys. We can safely remove this to make geovista work with both numpy 1.x and 2.x.

Closes #849

N.B., there appears to be some optional geovista dependencies holding back conda resolving the environment with numpy 2.x ... but that will untangle itself in the fullness of time, and isn't a blocker.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.30%. Comparing base (26b3a74) to head (4697148).
Report is 2 commits behind head on v0.5.x.

Additional details and impacted files

@@           Coverage Diff           @@
##           v0.5.x     #998   +/-   ##
=======================================
  Coverage   91.30%   91.30%           
=======================================
  Files          58       58           
  Lines        2934     2934           
=======================================
  Hits         2679     2679           
  Misses        255      255           

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