Checks for use of #![allow(...)] at the crate level.
Such uses cannot be overridden with --warn or --deny from the command line. They can
be overridden with --force-warn or --forbid, but one must know the #![allow(...)]
are present to use these unconventional options.
#![allow(clippy::assertions_on_constants)] // in code
Use instead:
// Allow `clippy::assertions-on-constants` in Cargo.toml. See:
// - https://doc.rust-lang.org/cargo/reference/manifest.html#the-lints-section
// - https://doc.rust-lang.org/clippy/configuration.html#lints-section-in-cargotoml