`significant_drop_in_scrutinee`: Fix false positives due to false drops of place expressions

Place expressions do not really create temporaries, so they will not create significant drops. For example, the following code snippet is quite good (rust-lang#8963):
```rust
fn main() {
    let x = std::sync::Mutex::new(vec![1, 2, 3]);
    let x_guard = x.lock().unwrap();
    match x_guard[0] {
        1 => println!("1!"),
        x => println!("{x}"),
    }
    drop(x_guard); // Some "usage"
}
```

Also, the previous logic thinks that references like `&MutexGuard<_>`/`Ref<'_, MutexGuard<'_, _>>` have significant drops, which is simply not true, so it is fixed together in this PR.

Fixes rust-lang/rust-clippy#8963
Fixes rust-lang/rust-clippy#9072

changelog: [`significant_drop_in_scrutinee`]: Fix false positives due to false drops of place expressions.

r? `@blyxyas`