[example][freeflowchannel] Rename exectuable

examples/freeflowchannel/CMakeLists.txt

 dune_symlink_to_source_files(FILES "params.input")
 
-dumux_add_test(NAME example_ff_channel
+dumux_add_test(NAME example_freeflow_channel_navierstokes
                LABELS freeflow navierstokes
                SOURCES main.cc
                CMAKE_GUARD HAVE_UMFPACK
@@ -8,4 +8,4 @@ dumux_add_test(NAME example_ff_channel
                CMD_ARGS       --script fuzzy
                               --files ${CMAKE_SOURCE_DIR}/test/references/example_ff_channel-reference.vtu
                                       ${CMAKE_CURRENT_BINARY_DIR}/example_ff_channel-00001.vtu
-                              --command "${CMAKE_CURRENT_BINARY_DIR}/example_ff_channel params.input -Problem.Name example_ff_channel")
+                              --command "${CMAKE_CURRENT_BINARY_DIR}/example_freeflow_channel_navierstokes params.input -Problem.Name example_ff_channel")