iwyu.yml: switched to Fedora to get the latest include-what-you-use / cleaned up includes
#15317
| Job | Run time |
|---|---|
| 5m 46s | |
| 2m 16s | |
| 5m 35s | |
| 1m 32s | |
| 5m 58s | |
| 2m 44s | |
| 6m 42s | |
| 2m 28s | |
| 33m 1s |