Suppress warnings about `int_bits_const`

[JohnTitor]

The build channels linux builder emits too many warnings about the int_bits_const feature:

 warning: a method with this name may be added to the standard library in the future
   --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.35/src/int/udiv.rs:98:23
    |
98  |             q = n << (<$ty>::BITS - sr);
    |                       ^^^^^^^^^^^
...
268 |         udivmod_inner!(n, d, rem, u128)
    |         ------------------------------- in this macro invocation
    |
    = warning: once this method is added to the standard library, the ambiguity may cause an error or change in behavior!
    = note: for more information, see issue #48919 <rust-lang/rust/issues/48919>
    = help: call with fully qualified syntax `Int::BITS(...)` to keep using the current method
    = help: add `#![feature(int_bits_const)]` to the crate attributes to enable `num::<impl u128>::BITS`
    = note: this warning originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)

The log on GHA is trunscated because of this, we should suppress this warning at least.

[JohnTitor]

This has been fixed by a recent compiler_builtins.