Adjust declare_interior_mutable_const lint's category

[SomeoneToIgnore]

Per the root readme, clippy::style is a category with

code that should be written in a more idiomatic way

description.

The code this lint guards from may be much worse than badly styled:

use std::sync::LazyLock;

// `const` instead of `static` causes `dbg!` to be printed 10 times
// instead of one.
const LICENSE_FILE_NAME_REGEX: LazyLock<String> = LazyLock::new(|| {
    dbg!("I am a large regex initialized in a lazy lock!");
    format!("Hello {}", "World".to_string())
});

fn main() {
    for _ in 0..10 {
        let _ = LICENSE_FILE_NAME_REGEX.split(" ");
    }
}

In large projects, it's unfortunate but sometimes possible to see style lints suppressed with

[workspace.lints.clippy]
style = { level = "allow", priority = -1 }

effectively turning off crucial checks for the code like above.

To keep them, promote this lint to clippy::suspicious:

code that is most likely wrong or useless

category that has the same, warn default level, thus not failing on false-positives which lead to #5863

---

changelog: [declare_interior_mutable_const]: promote lint's category to clippy::suspicious

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[y21]

Makes sense to me. I opened a thread on Zulip to give others a chance to comment on this: https://rust-lang.zulipchat.com/#narrow/channel/257328-clippy/topic/Moving.20declare_interior_mutable_const.20to.20suspicious

Will merge in a few days if nothing comes up.