`stdexec::env` brace-initializer with a single argument fails for `clang`

I don't have time to trace back this compiler failure but here is a Godbolt reproducer.

Basically, the code is:

#include "stdexec/execution.hpp"

struct CustomProperty
{
    template <typename Env> requires ::stdexec::tag_invocable<CustomProperty, Env>
    constexpr decltype(auto) operator()(Env&& env) const {
        return ::stdexec::tag_invoke(*this, std::forward<Env>(env));
    }
};

constexpr CustomProperty my_custom_property {};

int main()
{
    constexpr auto env = ::stdexec::env{::stdexec::prop{my_custom_property, 123}};

    static_assert(my_custom_property(env) == 123);
}

and with clang (19 or 20) it fails (gcc 13 also fails but gcc 15 is fine):

<source>:18:81: error: missing field '__elem1' initializer [-Werror,-Wmissing-field-initializers]
   18 |     constexpr auto env = ::stdexec::env{::stdexec::prop{my_custom_property, 123}};

I'm not sure whether this is due to a new recent commit but it used to work just fine a few weeks ago. Today I'm using e5dbe49a5257d29adee456f9f653acb00df634f5.

Start with the Godbolt reproducer using stdexec/execution.hpp and compare the clang 19/20 and GCC behavior at commit e5dbe49a5257d29adee456f9f653acb00df6345. Investigate why the single-argument stdexec::env initializer triggers -Wmissing-field-initializers, then verify that the example compiles and its static_assert passes under clang without breaking the GCC behavior.