Doc tests are failing on 1.51 for 0.11 release

[dignifiedquire]

See https://github.com/filecoin-project/blstrs/runs/5026964292?check_suite_focus=true

[str4d]

If someone wants to propose a patch to the 0.11 series to fix this, they can open a PR to do so. Otherwise, our MSRV is currently 1.56 and will soon be 1.63, so closing as stale.