Automatic toolchain upgrade to nightly-2026-01-08

[github-actions]

Update Rust toolchain from nightly-2026-01-07 to nightly-2026-01-08 without any other source changes.

[github-actions]

This is an automatically generated pull request. If any of the CI checks fail,
manual intervention is required. In such a case, review the changes at
https://github.com/rust-lang/rust from
rust-lang/rust@0aced20 up to
rust-lang/rust@fecb335. The log
for this commit range is:

https://github.com/rust-lang/rust/commit/fecb335cba Auto merge of #148339 - folkertdev:naked-macos-private-extern, r=Amanieu naked functions: emit `.private_extern` on macos

rust-lang/rust@fc546b94ad Auto merge of #150645 - GuillaumeGomez:rename-rustdoc-tests, r=Kobzol,Zalathar Rename tests/rustdoc into tests/rustdoc-html
rust-lang/rust@8256623ab4 Update rustc-dev-guide about tests/rustdoc renamed into tests/rustdoc-html
rust-lang/rust@a928f3352d Rename tests/rustdoc into tests/rustdoc-html
rust-lang/rust@84c84421cc Auto merge of #150759 - Kobzol:auto-branch, r=marcoieni Make verify-channel.sh script compatible with new bors
rust-lang/rust@6f7313e8ad Make verify-channel.sh script compatible with new bors
rust-lang/rust@d9617c8d9a Auto merge of #150310 - JonathanBrouwer:cfg_trace2, r=jdonszelmann