Fix bug in body forces code

[wilfonba]

Description

Fixes a bug in the body forces code.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

Scope

• This PR comprises a set of related changes with a common goal

How Has This Been Tested?

Ran a 2D Rayleigh-Taylor instability with and without this correction on Wingtip using NVHPC/23.11. The video shows the old solution on the left and the solution with the correction on the right. The picture shows a comparison with linear theory on a semilogy and loglog plot. The slope of the solution with the bug fix matches that of the linear theory more closely than the old code with a bug.

https://github.com/user-attachments/assets/923f12e5-21ce-4b8a-98db-46298913749f

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 54.38%. Comparing base (75f5e3b) to head (69cc8cb).
Report is 12 commits behind head on master.

Files with missing lines	Patch %	Lines
src/simulation/m_time_steppers.fpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #661   +/-   ##
=======================================
  Coverage   54.38%   54.38%           
=======================================
  Files          61       61           
  Lines       13751    13751           
  Branches     1720     1719    -1     
=======================================
  Hits         7478     7478           
  Misses       5817     5817           
  Partials      456      456           

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