common/build-style/cargo.sh: use offline install

[0x5c]

This prevents cargo install from wasting time fetching the crate registry.

[CI skip]

Testing the changes

• I tested the changes in this PR: YES

[ericonr]

Please don't add [ci skip] to the commit itself, it's enough in the PR description.

Which packages have you tested with this?

[0x5c]

Please don't add [ci skip] to the commit itself, it's enough in the PR description.

It got there because I was writing my commit message in so it could be the PR message as-is. Didn't think it fully through tho. I can remove it if you want

Which packages have you tested with this?

I tested it with riff (#37013), but it should work for everything else since fetching the registry in the install phase doesn't have an effect in the first place because we use --locked in the install. So this gets rid of a long networked no-op that can fail (the Updating crates.io index line in the install phase).

[ericonr]

I can remove it if you want

Please do :)

I'm going to try and test this around a bit.

[0x5c]

The commit message has been cleaned