Bluetooth: tests: shell: Add missing dependency in mesh.conf

Add missing dependency in mesh.conf.
Handles this warning: Warning: BT_MESH_SHELL was assigned the value 'y'
but got the value 'n'. Check these unsatisfied dependencies:
BT_MESH_HEALTH_CLI (=n)

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>