`rls` no longer builds after rust-lang/rust#60874

[rust-highfive]

Hello, this is your friendly neighborhood mergebot.
After merging PR #60874, I observed that the tool rls no longer builds.
A follow-up PR to the repository https://github.com/rust-lang/rls is needed to fix the fallout.

cc @ehuss, do you think you would have time to do the follow-up work?
If so, that would be great!

cc @alexcrichton, the PR reviewer, and @rust-lang/compiler -- nominating for prioritization.

[alexcrichton]

cc @rust-lang/release as well, this is likely to impact the beta branch next week.

Additionally changes to checkregression.py need to be backed out ASAP (e.g. during and after the beta branch)

[oli-obk]

fixed in #60946