Fix __exit__ return type of various context managers
#1317
| Job | Run time |
|---|---|
| 7s | |
| 1m 8s | |
| 16s | |
| 17s | |
| 1m 3s | |
| 1m 9s | |
| 1m 15s | |
| 1m 18s | |
| 1m 49s | |
| 1m 18s | |
| 1m 4s | |
| 1m 32s | |
| 2m 22s | |
| 4s | |
| 14m 42s |