[porousmediumflow][2pncmin][nonisothermal] Use current permeability for Neumann gas flux

In the non-isothermal 2pncmin test the reference permeability is used in the problem for calculating the Neumann flux of the component air. However, the permeability changes during the simulation due to the precipitation of salt.

Therefore, I propose to use the current permeability here:

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*volVars.permeability()

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*volVars.permeability()

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