Fix Rust output regression

[Integralist]

NOTE: This was first seen in CI but can be reproduced by uninstalling all toolchains (e.g. rustup toolchain uninstall <toolchain>) and then running rustup show active-toolchain (see output below). The CLI was expecting one line of output but in fact there is now multiple lines, and the line we're interested in is actually the last line of output.

info: syncing channel updates for 'stable-aarch64-apple-darwin'
info: latest update on 2022-09-22, rust version 1.64.0 (a55dd71d5 2022-09-19)
info: downloading component 'cargo'
info: downloading component 'clippy'
info: downloading component 'rust-docs'
 18.8 MiB /  18.8 MiB (100 %)  11.3 MiB/s in  1s ETA:  0s
info: downloading component 'rust-std'
 25.6 MiB /  25.6 MiB (100 %)  10.5 MiB/s in  2s ETA:  0s
info: downloading component 'rustc'
 49.1 MiB /  49.1 MiB (100 %)   9.6 MiB/s in  5s ETA:  0s
info: downloading component 'rustfmt'
info: installing component 'cargo'
info: installing component 'clippy'
info: installing component 'rust-docs'
 18.8 MiB /  18.8 MiB (100 %)   6.4 MiB/s in  2s ETA:  0s
info: installing component 'rust-std'
 25.6 MiB /  25.6 MiB (100 %)  18.3 MiB/s in  1s ETA:  0s
info: installing component 'rustc'
 49.1 MiB /  49.1 MiB (100 %)  20.8 MiB/s in  2s ETA:  0s
info: installing component 'rustfmt'
stable-aarch64-apple-darwin (default)

[triblondon]

I wonder about maybe filtering out lines that start with whitespace or 'info:', or investigating whether there's an option for this command to be less verbose so it doesn't print the syncing output? But assuming those are not viable / considered less optimal solutions, this is good!