samples: stm32 serial wakeup: Don't run on stm32l562e_dk in CI

On STM32 PM serial wakeup sample, a power efficient configuration using
lpuart is provided for stm32l562e_dk target.
Though, since default configuration of the board is using ST-Link virtual
port com on uart1, which can't be changed in CI and hence can't be tested,
then remove this target from sample yaml configuration.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>