Queue was not locked when building `empty-library` failed

[Nemo157]

Sep 22 00:59:23 docsrs cratesfyi[28969]: 2023-09-22T00:59:23.845933Z  INFO docs_rs::docbuilder::rustwide_builder: building a dummy crate to get essential files
[...]
Sep 22 00:59:42 docsrs cratesfyi[28969]: 2023-09-22T00:59:42.825956Z  INFO log: [stderr] error: Unrecognized option: 'disable-per-crate-search' log.target="rustwide::cmd" log.module_pa
[...]
Sep 22 00:59:42 docsrs cratesfyi[28969]: 2023-09-22T00:59:42.827877Z  INFO log: [stderr]   process didn't exit successfully: `/opt/rustwide/rustup-home/toolchains/nightly-x86_64-unknow
[...]
Sep 22 00:59:42 docsrs cratesfyi[28969]: 2023-09-22T00:59:42.931373Z  WARN docs_rs::utils: got error on attempt 1, will try again after 2s:
Sep 22 00:59:42 docsrs cratesfyi[28969]: Updating toolchain failed, locking queue
Sep 22 00:59:42 docsrs cratesfyi[28969]: Caused by:
Sep 22 00:59:42 docsrs cratesfyi[28969]:     failed to build dummy crate for rustc 1.74.0-nightly (b3aa8e716 2023-09-21)
[...]

But it continued on to build more crates anyway.

[Nemo157]

Ah, because we retry updating the toolchain to workaround network issues. The problem is if it succeeds to download the new toolchain, but then fails to add essential files, the next time it already has the updated toolchain and succeeds.