fix_lint action fails due to outdated proc-macro2

Example: https://github.com/element-hq/synapse/actions/runs/16507822915/job/46682893706

According to https://github.com/rust-lang/rust/issues/113152 this is due to a nightly feature no longer existing, which on the surface appears as though would be true: the CI is trying to install/compile proc-macro2 v1.0.51 when the `Cargo.lock` files throughout the project want v1.0.89 or higher. I don't know where it's getting `.51` from, but according to https://github.com/rust-lang/rust/issues/113152#issuecomment-1612580132 the issue is fixed in `.60`+.