Correct type instability in fluxes computation

[simone-silvestri]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 0.00%. Comparing base (c6bffe7) to head (dfccf76).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...Models/CrossRealmFluxes/atmosphere_ocean_fluxes.jl	0.00%	9 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #321   +/-   ##
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  Coverage   0.00%   0.00%           
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  Files         34      34           
  Lines       1983    1983           
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  Misses      1983    1983           

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[glwagner]

I don't think causes an issue since it gets convertd in setindex but its a good idea anyways