Spectator mode players can be killed by the /kill command

Players in Spectator mode (/gamemode spectator) are intended to be completely invulnerable and unable to interact with the world. However, executing the /kill command targeting a spectator player successfully kills them, which is inconsistent with the expected behavior of Spectator mode.

Steps to reproduce:

1. Create a new world and enable cheats.

2. Switch the game mode to Spectator mode using /gamemode spectator.

3. Open the chat and execute the command /kill @s.

4. Observe that you are killed and forced to respawn, despite being in Spectator mode.