Add a test for #71202

[osa1]

Closes #71202

---

Note that the test normally generates this warning:

warning: cannot use constants which depend on generic parameters in types
  --> test.rs:10:5
   |
10 | /     const ITEM_IS_COPY: [(); 1 - {
11 | |         trait NotCopy {
12 | |             const VALUE: bool = false;
13 | |         }
...  |
26 | |         <IsCopy<T>>::VALUE
27 | |     } as usize] = [];
   | |_____________________^
   |
   = note: `#[warn(const_evaluatable_unchecked)]` on by default
   = 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>

I added allow(const_evaluatable_unchecked), but maybe we just don't want to add a test for this as the program is not really valid?

[rust-highfive]

r? @Mark-Simulacrum

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[jonas-schievink]

@bors r+

[bors]

📌 Commit 5f1a7aa has been approved by jonas-schievink

[jonas-schievink]

@bors rollup