samples/boards/stm32: blinky: Limit execution on stm32 lptim enabled
samples/boards/stm32: blinky: Limit execution on stm32 lptim enabled

Restrict sample execution in CI to boards that have
"st,stm32-lptim" enabled so we're sure it is a STM32 target.

Signed-off-by: Erwan Gouriou <de4d967452b83bb0e37525652734e7d9163b6a4c@linaro.org>

zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr