twister: Fix trivial typo
twister: Fix trivial typo

Plarforms -> Platforms

Signed-off-by: Olof Johansson <8c69ee23f3f44f8162a64d579c1fa25c2f55298a@lixom.net>

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