Auto merge of #1864 - hyd-dev:rustup, r=RalfJung

Update cargo-miri test

The doctest output was [changed](https://github.com/rust-lang/miri/runs/3238758260?check_suite_focus=true#step:8:1263) (probably by https://github.com/rust-lang/cargo/pull/9730). Update `test-cargo-miri/test.default.stdout.ref` to match the new output.