fix &str type check in from_str_radix_10

[zihan0822]

minor fix in from_str_radix_10 lint, is_type_diagnostic_item only checks Adt, use .is_str() instead

changelog: [from_str_radix_10]: properly lint references to &str as well

[rustbot]

r? @samueltardieu

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[samueltardieu]

Could you add a test where that makes a difference in output? Such as:

    let string = &&&"300";
    i32::from_str_radix(&string, 10)?;

[zihan0822]

Done! @rustbot ready

[samueltardieu]

Thanks.