Why don't we have a means of determining if something is a lambda?

template<typename Lambda>
requires std::is_lambda_v<Lambda>
struct OnScopeExit {
    Lambda f;
    OnScopeExit(Lambda arg) : f(arg) {}
    ~OnScopeExit(void) { f(); }
};

void Func(void) { }

int main(void)
{
    OnScopeExit myguard([](){ /* Do Something */ });
}