`const_evaluatable_unchecked` incorrectly triggers when capturing return type of parent const block

fn main() {
    const {
        [0; const { 0 }];
    }
    
    const {
        [0; {
            let _ = || ();
            0
        }];
    }
}

results in

warning: cannot use constants which depend on generic parameters in types
 --> src/main.rs:3:13
  |
3 |         [0; const { 0 }];
  |             ^^^^^^^^^^^
  |
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #76200 <https://github.com/rust-lang/rust/issues/76200>
  = note: `#[warn(const_evaluatable_unchecked)]` (part of `#[warn(future_incompatible)]`) on by default

warning: cannot use constants which depend on generic parameters in types
  --> src/main.rs:7:13
   |
 7 |           [0; {
   |  _____________^
 8 | |             let _ = || ();
 9 | |             0
10 | |         }];
   | |_________^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #76200 <https://github.com/rust-lang/rust/issues/76200>

This is a false positive and we should not lint here.

Issue discovered by @edwloef in #76200

Start by compiling the reproducer in src/main.rs and compare the two const-block cases under the const_evaluatable_unchecked lint. Trace where the lint is emitted for these expressions; done means neither case produces this false-positive warning, with regression coverage for the behavior.