samples: sensor: sensor_shell: update pytest to validate fix

Update the pytest script to exercise the entire
`sensor_channel_name` table with `parse_named_int()`.

The `gauge_desired_charging_current` is selected because
it is the last one in the table before `all`, `all` is not
used because `sensor get sensor@0 all` doesn't return anything.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>