Use rust-lang/rust instead of rust-lang-ci/rust for unrolled rollup build commit URLs

[Kobzol]

We have moved CI from rust-lang-ci/rust to rust-lang/rust, so this can be merged now.

Context: rust-lang/infra-team#188

[lqd]

CI commits don't usually last that long before being GCed by github, but will this impact bisecting through recent rollups that were still using rust-lang-ci?

[Kobzol]

I guess it could, yeah. It's just the URL that would be wrong. We could either provide both links, or test if the link is 404 (?), or add some check based on the date of the commit.

[lqd]

Maybe by the time this is merged, released, and people update there will be no more of these old CI commits to worry about 😅 -- and just the PR name itself will be found (which should be enough IME).

Otherwise this LGTM.

Spelling out the situation a bit in the changelog should be helpful in any case.

[Kobzol]

Added a changelog entry and also the second URL in the printed log.

[ehuss]

Thanks! I forget how long the perf builds are available (is it the same as regular commits?). I assume we can essentially revert this after that time?

[Kobzol]

It should essentially be a regular try build commit, yeah.