Fix typo in name of 'run_background_tasks_on' option in config manual (#12749)

changelog.d/12749.doc

@@ -0,0 +1 @@
+Fix typo in 'run_background_tasks_on' option name in configuration manual documentation.

docs/usage/configuration/config_documentation.md

@@ -3454,7 +3454,7 @@ stream_writers:
   typing: worker1
 ```
 ---
-Config option: `run_background_task_on`
+Config option: `run_background_tasks_on`
 
 The worker that is used to run background tasks (e.g. cleaning up expired
 data). If not provided this defaults to the main process.