doc: clarify async caveats for events.once()
#80361
| Job | Run time |
|---|---|
| 34m 20s | |
| 2h 31m 42s | |
| 3h 6m 2s |
events.once()
#80361
| Job | Run time |
|---|---|
| 34m 20s | |
| 2h 31m 42s | |
| 3h 6m 2s |