ci: manifest: Drop west label for manifest updates
ci: manifest: Drop west label for manifest updates

This commit updates the manifest workflow to not label the pull
requests updating the west manifest (`west.yml`) with the `west` label
because the `manifest` label alone is enough for this purpose and the
`west` label can be easily confused with the `area: West` label.

Signed-off-by: Stephanos Ioannidis <dc76e9f0c0006e8f919e0c515c66dbba3982f785@stephanos.io>

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