[T/GWF] Rename update expected solution.

- Rename to better reflect the contained date.
- Expected solution update due to output of specific flux instead of flux.

ProcessLib/GroundwaterFlow/Tests.cmake

@@ -297,7 +297,7 @@ AddTest(
     TESTER vtkdiff
     REQUIREMENTS NOT OGS_USE_MPI
     DIFF_DATA
-    cube_1x1x1_prism_2e3_complete_surface.vtu cube_1x1x1_prism_2e3_complete_surface_front_back_dirichlet_surfaceflux_t_1.000000.vtu surfaceflux_front_back_reference surfaceflux_front_back 1e-15 1e-15
+    cube_1x1x1_prism_2e3_complete_surface_front_back_dirichlet_specific_flux_t_1.000000.vtu cube_1x1x1_prism_2e3_complete_surface_front_back_dirichlet_specific_flux_t_1.000000.vtu specific_flux specific_flux  1e-15 1e-15
 )
 
 AddTest(

Tests/Data/Elliptic/cube_1x1x1_GroundWaterFlow/cube_2e3_prism_surfaceflux_front_back.prj

@@ -20,8 +20,8 @@
             </secondary_variables>
             <calculatesurfaceflux>
                 <mesh>cube_1x1x1_prism_2e3_complete_surface</mesh>
-                <property_name>surfaceflux_front_back</property_name>
-                <output_mesh>cube_1x1x1_prism_2e3_complete_surface_front_back_dirichlet_surfaceflux.vtu</output_mesh>
+                <property_name>specific_flux</property_name>
+                <output_mesh>cube_1x1x1_prism_2e3_complete_surface_front_back_dirichlet_specific_flux.vtu</output_mesh>
             </calculatesurfaceflux>
         </process>
     </processes>