Only test register_handler in a single thread
#9352
| Job | Run time |
|---|---|
| 7m 18s | |
| 3m 45s | |
| 2m 41s | |
| 3m 40s | |
| 3m 4s | |
| 3m 33s | |
| 7m 48s | |
| 4m 8s | |
| 4m 29s | |
| 4m 46s | |
| 4m 22s | |
| 4m 32s | |
| 4m 9s | |
| 7m 41s | |
| 1s | |
| 1h 5m 57s |