Fix __exit__ return type of various context managers
#1340
| Job | Run time |
|---|---|
| 3s | |
| 20s | |
| 1m 10s | |
| 1m 4s | |
| 1m 10s | |
| 12s | |
| 1m 21s | |
| 1m 28s | |
| 1m 4s | |
| 1m 49s | |
| 1m 19s | |
| 1m 11s | |
| 1m 42s | |
| 2m 40s | |
| 5s | |
| 16m 38s |