boards: nordic: nrf54l09pdk: Change pin used for led0

P1.7 used for led 0 was not passing gpio_api_1pin test (probably
shortened with another pin in the test setup. Use different pin
that passes the gpio_api_1pin test. At current stage this PDK is
'virtual' so this pin is not attached to any LED and it can be
changed.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>