Rollup merge of #92037 - fee1-dead:fix_env_dmbic, r=oli-obk

Use a const ParamEnv when in default_method_body_is_const

r? `@oli-obk`

This PR fixes the param_env function to return `constness: Const` correctly for trait methods marked with `#[default_method_body_is_const]`. The snippet below is erroneously accepted by the compiler and has been fixed by this change. ([Playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=12dc6681b2eeee5f604203d96259eeb4))

```rust
#![feature(const_fn_trait_bound)]
#![feature(const_trait_impl)]

trait Tr {}
impl Tr for () {}

const fn foo<T>() where T: ~const Tr {}

pub trait Foo {
    #[default_method_body_is_const]
    fn foo() {
        foo::<()>();
    }
}
```

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