fix(examples): fix modflow boundaries example name

[wpbonelli]

thanks @kerrybardot for pointing out, looks like I did this by accident https://github.com/modflowpy/flopy/commits/1545f6334d6c045856b691a4732a7ae5ba034fad/examples/Notebooks/flopy3_modflow_boundaries.ipynb?browsing_rename_history=true&new_path=.docs/Notebooks/flopy3_lake_example.ipynb&original_branch=0c6e2f797e374d64c60b25cdd73fdfd05d711094

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.2%. Comparing base (556c088) to head (f3f9ec7).
⚠️ Report is 33 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2579      +/-   ##
===========================================
+ Coverage     55.5%    72.2%   +16.7%     
===========================================
  Files          644      643       -1     
  Lines       124135   122150    -1985     
===========================================
+ Hits         68947    88307   +19360     
+ Misses       55188    33843   -21345     

see 383 files with indirect coverage changes

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