Add test coverage for Non-conservative BC do nothing

[MarcoArtiano]

No description provided.

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.88%. Comparing base (ba30bb3) to head (d6f99fc).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2269      +/-   ##
==========================================
+ Coverage   96.88%   96.88%   +0.01%     
==========================================
  Files         490      490              
  Lines       39491    39491              
==========================================
+ Hits        38257    38260       +3     
+ Misses       1234     1231       -3     

Flag	Coverage Δ
unittests	96.88% <ø> (+0.01%)	⬆️

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[MarcoArtiano]

By the way, Base.isapprox don't accept tuples, so we might define a new method for it, for instance

function Base.isapprox(x::Tuple, y::Tuple;
    atol::Real=0, rtol::Real=rtoldefault(x,y,atol),
    nans::Bool=false, norm::Function=abs)
x′, = promote(x)
y′, = promote(y)
x == y ||
(all(isfinite.(x)) && all(isfinite.(y)) && Trixi.norm.(x .- y) <= max(ntuple(_ -> atol, length(x)), rtol.*max(Trixi.norm.(x′), Trixi.norm.(y′)))) ||
(nans && isnan(x) && isnan(y))
end

to keep everything cleaner, so that

test_bc_out = boundary_condition_do_nothing(u, outward_direction, x, t,
                                                    surface_fluxes,
                                                    equations)
        @test surface_fluxes[1](u, outward_direction, equations) ≈ test_bc_[1]
        @test surface_fluxes[2](u, outward_direction, equations) ≈ test_bc_[2]

will look like

@test surface_fluxes(u, outward_direction, equations)  ≈ boundary_condition_do_nothing(u, outward_direction, x, t,
                                                    surface_fluxes,
                                                    equations)

[ranocha]

We should not do that since that's type piracy.