fix(binarygrid_util): restore top assignment dropped with reshape

[wpbonelli]

Fix #2831. #2794 switched several places where .shape was set directly to .reshape() calls instead, but dropped an assignment on one of them.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.5%. Comparing base (556c088) to head (7d41a7b).
⚠️ Report is 216 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2833      +/-   ##
===========================================
+ Coverage     55.5%    73.5%   +18.0%     
===========================================
  Files          644      659      +15     
  Lines       124135   132188    +8053     
===========================================
+ Hits         68947    97220   +28273     
+ Misses       55188    34968   -20220     

Files with missing lines	Coverage Δ
flopy/mf6/utils/binarygrid_util.py	89.6% <100.0%> (-1.2%)	⬇️

... and 584 files with indirect coverage changes

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