Fix condition for richards laytyp check in mfusglpf.py

[martinvonk]

This check (self.laytyp==5) always defaults to False as self.laytyp is a MFArray due to the super().__init__. Therefore, if laytyp=5 parsed to the MfUsgLpf.init, self.richards will always be False and unsaturated flow won't be simulated.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.3%. Comparing base (556c088) to head (9e30eb9).
⚠️ Report is 204 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2812      +/-   ##
===========================================
+ Coverage     55.5%    73.3%   +17.7%     
===========================================
  Files          644      659      +15     
  Lines       124135   132182    +8047     
===========================================
+ Hits         68947    96907   +27960     
+ Misses       55188    35275   -19913     

Files with missing lines	Coverage Δ
flopy/mfusg/mfusglpf.py	74.0% <100.0%> (-6.4%)	⬇️

... and 584 files with indirect coverage changes

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