Improve handling of masks in concatenate

[bouweandela]

🚀 Pull Request

Description

The following arrays compare equal in iris.util.array_equal, so they should also compare equal in the hash function used by concatenate:

• np.array([1, 2]) and np.ma.array([1, 2], mask=np.ma.nomask)
• np.array([1, 2]) and np.ma.array([1, 2], mask=[0, 0])
• np.ma.array([1, 2], mask=[0, 0]) and np.ma.array([1, 2], mask=np.ma.nomask)

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.82%. Comparing base (dd0432e) to head (b79bdde).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6187   +/-   ##
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  Coverage   89.82%   89.82%           
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  Files          88       88           
  Lines       23185    23185           
  Branches     4314     4314           
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  Hits        20825    20825           
  Misses       1628     1628           
  Partials      732      732           

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[trexfeathers]

Thanks @bouweandela, this makes sense to me