Update btstep negative eta warning

[awallcraft]

In Boussinesq mode the eta below bathyT warning includes the location, but in non-Boussinesq mode the corresponding negative eta warning does not.

Added the location to the negative eta warning.

No answers are changed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 21.69%. Comparing base (5e4f97b) to head (e13b8f7).
Report is 1 commits behind head on dev/gfdl.

❗ There is a different number of reports uploaded between BASE (5e4f97b) and HEAD (e13b8f7). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (5e4f97b)	HEAD (e13b8f7)
	2	1

Additional details and impacted files

@@              Coverage Diff              @@
##           dev/gfdl     #844       +/-   ##
=============================================
- Coverage     38.10%   21.69%   -16.41%     
=============================================
  Files           298      137      -161     
  Lines         87711    33202    -54509     
  Branches      16447     5951    -10496     
=============================================
- Hits          33418     7202    -26216     
+ Misses        48264    25443    -22821     
+ Partials       6029      557     -5472     

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[Hallberg-NOAA]

Thank you very much for this useful functional improvement in the information content of these error messages.

My only very minor quibble here is that the MOM6 style guide at https://github.com/mom-ocean/MOM6/wiki/Code-style-guide#white-space strongly encourages the use of 4 or more spaces of indenting for continuation lines, rather than the 2 lines as used here.

[Hallberg-NOAA]

Thank you for this valuable enhancement to add information content to an error message.

[Hallberg-NOAA]

This PR has passed pipeline testing at https://gitlab.gfdl.noaa.gov/ogrp/mom6ci/MOM6/-/pipelines/26602.