fix: `let-and-return` suggests invalid cast (#16135)

[ErinvanderVeen]

Simple PR that handles a special case where a raw pointer was invalidly cast via as _.

First PR, would appreciate feedback.

changelog: [let_and_return]: fix lint suggestion for invalid cast to raw pointer.

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  • 8a0f8d1547967d2eb12517fa4cda2680d2dc4c68

[Jarcho]

The test you have still works with the extra cast, it's just unnecessary. The type cast is needed to work around deficiencies in type inference:

struct S;
trait T {}
impl T for S {}

fn f(x: *const S) -> *const dyn T {
    Clone::clone(&x) as _
}

[rustbot]

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