fix: update numpy array comparisons to use isin

[emmanuel-ferdman]

PR Summary

This small PR resolves the deprecation warnings coming from np.in1d:

/home/runner/work/flopy/flopy/flopy/utils/zonbud.py:1031: DeprecationWarning: `in1d` is deprecated. Use `np.isin` instea

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.1%. Comparing base (7eb7c88) to head (3e99258).
Report is 13 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2504      +/-   ##
===========================================
- Coverage     76.1%    56.1%   -20.1%     
===========================================
  Files          296      640     +344     
  Lines        64215   124323   +60108     
===========================================
+ Hits         48885    69747   +20862     
- Misses       15330    54576   +39246     

Files with missing lines	Coverage Δ
flopy/utils/zonbud.py	66.8% <ø> (ø)

... and 475 files with indirect coverage changes

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[wpbonelli]

thanks!