Pin indexmap back to account for hashbrown MSRV bump
#1135
| Job | Run time |
|---|---|
| 11m 53s | |
| 8m 35s | |
| 11m 39s | |
| 11m 58s | |
| 9m 53s | |
| 11m 16s | |
| 6m 59s | |
| 6m 20s | |
| 11m 40s | |
| 1h 30m 13s |