Log versions during self updates

[djc]

Fixes #4327.

[rami3l]

LGTM, thanks a lot :)

[rami3l]

I just noticed that during rustup self update we already have this message:

rustup/src/cli/self_update.rs

Lines 1063 to 1067 in 7ba0abf

	let _ = common::show_channel_update(
	cfg,
	PackageUpdate::Rustup,
	Ok(UpdateStatus::Updated(version)),
	);

... so it might be interesting to just reuse that logic here.

[djc]

I just noticed that during rustup self update we already have this message:

I noticed that too, but I think just showing these versions as soon as we have them is probably better.