Command server output in singleplayer is printed into chat

The Bug:

Command server output in singleplayer is printed into chat.

This issue was not present in 24w38a.

Steps to Reproduce:

1. Load into a singleplayer world and run any command.
2. Observe how two lines are printed in chat; the command feedback, and the server admin log.

Observed Behavior:

Command server output in singleplayer is printed into chat.

Expected Behavior:

Command server output in singleplayer would not be printed into chat.