ci: semver checks fail with a compiler error

[agilarity]

Problem

Semver Check began failing with this kind of error 5 days ago.

error[E0658]: `#[diagnostic]` attribute name space is experimental
   --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/axum-0.7.5/src/handler/mod.rs:130:5
    |
130 |     diagnostic::on_unimplemented(
    |     ^^^^^^^^^^
    |
    = note: see issue #111[99](https://github.com/leptos-rs/leptos/actions/runs/8486766252/job/23253797016#step:3:100)6 <https://github.com/rust-lang/rust/issues/111996> for more information
    = help: add `#![feature(diagnostic_namespace)]` to the crate attributes to enable
    = note: this compiler was built on 2024-01-27; consider upgrading it if it is out of date

For more information about this error, try `rustc --explain E0658`.
error: could not compile `axum` (lib) due to 1 previous error

Observations

• I reproduced the problem locally, even against a known good commit (5819014c).
• The blame seems to fall outside the leptos code.

Workaround

• I can submit a PR tomorrow to disable the semver checks for now.
• FYI: @gbj @benwis