Use Numpy rng in NSEM tests

[santisoler]

Summary

Replace the usage of the deprecated functions in numpy.random module for the Numpy's random number generator class and its methods, in most of the NSEM tests.

PR Checklist

• If this is a work in progress PR, set as a Draft PR
• Linted my code according to the style guides.
• Added tests to verify changes to the code.
• Added necessary documentation to any new functions/classes following the
  expect style.
• Marked as ready for review (if this is was a draft PR), and converted
  to a Pull Request
• Tagged @simpeg/simpeg-developers when ready for review.

Reference issue

Part of the solution to #1289

What does this implement/fix?

Additional information

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.23%. Comparing base (fb10cda) to head (afbac95).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1450      +/-   ##
==========================================
+ Coverage   85.77%   86.23%   +0.45%     
==========================================
  Files         390      396       +6     
  Lines       49669    50327     +658     
  Branches     5290     5308      +18     
==========================================
+ Hits        42606    43401     +795     
+ Misses       5626     5474     -152     
- Partials     1437     1452      +15     

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