[test][porousmediumflow][2pncmin][nonisothermal] Neumann flux at top has to be adapted

Within in the non-isothermal 2pncmin test a few things for the Neumann BC at the top should be adapted:

1. In the upwind term (here) the reference mass-specific density of air is used, but there should be the molar density of air. With the mass-specific density \rho = 1.2 ~\text{kg}/\text{m}^3 and the molar mass of air M=28.96 * 10^{-3} ~\text{kg}/\text{mol}, we have \rho^{\text{mol}}=\rho/M \approx 41,44 ~\text{mol}/\text{m}^3
2. The density of air (e.g. here) for the liquid flux should generally be harmonic averaged if CCFV is used with TPFA and arithmetic averaged for box method (as flux for liquid phase is purely diffusive and we do upwind just for advective processes)
3. The comments for "gas flux in/out" (here) should be switched.
4. For the energy exchange the harmonic mean of the effective heat conductivity within the porous medium and the heat conductivity within the free-flow should be taken. (Note, that applying the same harmonic averaging for the diffusion coefficient is counter-productive as the effective diffusion coefficient, using Millington-Quirk, is small for highly water-saturated porous media. This would lead to a lower evaporation rate for highly water saturated porous-media in comparison to high evaporation rates for almost dried-out porous media. Hence, only the pure binary diffusion coefficient is taken - It could be scaled e.g. linearly with the porosity)