gh: ext-source: Fix typo
gh: ext-source: Fix typo

Spell "maintaining" correctly.

Signed-off-by: Carles Cufi <853081dc8dca4fe6a7e3c984752718b5db36e060@nordicsemi.no>

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