[test] avoid deprecation warning from neumann interface

test/freeflow/shallowwater/dambreak/problem.hh

test/geomechanics/elastic/problem.hh

test/multidomain/boundary/darcydarcy/1p_1p/problem.hh

test/multidomain/boundary/darcydarcy/1p_2p/problem.hh

...esdarcy/1p2c_1p2c/diffusionlawcomparison/problem_darcy.hh

...ltidomain/boundary/stokesdarcy/1p2c_1p2c/problem_darcy.hh

...ltidomain/boundary/stokesdarcy/1p2c_2p2c/problem_darcy.hh

...ltidomain/boundary/stokesdarcy/1p3c_1p3c/problem_darcy.hh

test/multidomain/boundary/stokesdarcy/1p_1p/problem_darcy.hh

test/multidomain/boundary/stokesdarcy/1p_2p/problem_darcy.hh

test/multidomain/embedded/1d3d/1p2c_richards2c/main.cc

...multidomain/embedded/1d3d/1p2c_richards2c/problem_root.hh

test/multidomain/embedded/1d3d/1p_richards/problem_root.hh

test/multidomain/facet/1p_1p/analytical/problem_bulk.hh

test/multidomain/facet/1p_1p/gravity/problem_bulk.hh

test/multidomain/facet/1p_1p/linearprofile/problem_bulk.hh

test/multidomain/facet/tracer_tracer/problem_1p_bulk.hh

test/multidomain/facet/tracer_tracer/problem_tracer_bulk.hh

.../multidomain/facet/tracer_tracer/problem_tracer_lowdim.hh

...ediumflow/1p/implicit/nonisothermal/problem_convection.hh