Fix FP in inherent_to_string when the function has generic parameters

[MortenLohne]

Minimal example of the false positive:

struct G;

impl G {
    fn to_string<const _N: usize>(&self) -> String {
        "G.to_string()".to_string()
    }
}

fn main() {
    let g = G;
    g.to_string::<1>();
}

Clippy emits an inherent_to_string warning, and suggests that we implement Display for G instead. However, this is not possible, since the generic parameter _N only exists in this function, not in G itself. This particular example uses const generics, which is where the issue is most likely to come up, but this PR skips the lint if the to_string function has any kind of generic parameters.

changelog: Fix FP in inherent_to_string

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @flip1995 (or someone else) soon.

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[flip1995]

@bors r+

Thanks! And welcome to Clippy 🎉

[bors]

📌 Commit 19a3775 has been approved by flip1995

[bors]

⌛ Testing commit 19a3775 with merge 728f397...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing 728f397 to master...