Update to 0.6.11 breaks my build

[Jonathan 'theJPster' Pallant]

I noticed by Github actions were failling: https://github.com/Neotron-Compute/Neotron-32-BIOS/runs/409621382?check_suite_focus=true

error: missing documentation for a function
   --> src/main.rs:266:1
    |
266 | #[entry]
    | ^^^^^^^^
    |
note: lint level defined here
   --> src/main.rs:100:9
    |
100 | #![deny(missing_docs)]
    |         ^^^^^^^^^^^^

error: aborting due to previous error

error: could not compile `neotron_32_bios`.

This worked fine on 0.6.10. My #[entry] function has documentation:

/// Entry point to the BIOS. This is called from the reset vector by
/// `cortex-m-rt`.
#[entry]
fn main() -> ! {
    ...
}

[Jonas Schievink]

Fixed in 0.6.12.