UnexpectedVersionFormat installing nightly-2020-10-23

[Michael-F-Bryan]

While troubleshooting rust-lang/rust#81221 I ran into a panic in cargo-bisect-rust where it encountered a UnexpectedVersionFormat error while installing nightly-2020-10-23.

$ cargo bisect-rustc --preserve --start 2020-07-27 --verbose -- build
installing nightly-2020-07-27
testing...
RESULT: nightly-2020-07-27, ===> No

installing nightly-2021-01-19
testing...
RESULT: nightly-2021-01-19, ===> Yes

installing nightly-2020-10-23
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: UnexpectedVersionFormat', /home/michael/.cargo/registry/src/github.com-1ecc6299db9ec823/cargo-bisect-rustc-0.6.0/src/toolchains.rs:91:58
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

The annoying part is that I tried to run it again with RUST_BACKTRACE=1, and installing nightly-2020-10-23 completed without an issue.

[cormacrelf]

For me this was because of something attempting to read my rust-toolchain.toml, which had an invalid channel name in it.