Compiler ICE when accessing `self[i]` where `self` is defined using const generics `[T;N]`

[ironcev]

#7601 introduces a should_pass/language/const_generics_array_in_reassignments tests with the following code snippet:

impl<T, const N: u64> DefaultSelf<T> for [T; N]
where
    T: AbiEncode + PartialEq,
{
    fn default_self(ref mut self, default: T) {
        let mut i = 0;
        while i < N {
            self[i] = default;             // <<<<---- This works as expected.
            assert_eq(self[i], default);   // <<<<---- This causes ICE.
            i += 1;
        }
    }
}

The self[i] access in the assert_eq results in:

assert_eq(self[i], default);
          ^^^^ Internal compiler error: Unsupported array value for index expression.