This is being emitted with [GCC 10.2.1](https://packages.debian.org/bullseye/g++-arm-linux-gnueabihf), in some CI jobs: i.e https://github.com/bitcoin/bitcoin/pull/25972/checks?check_run_id=12423693655, or https://github.com/bitcoin/bitcoin/pull/25972/checks?check_run_id=12423693651 (where we actually turn on all our warning flags with depends builds).
```bash
In file included from test/miniscript_tests.cpp:19:
./script/miniscript.h:1197:71: error: comparison of integers of different signs: 'typename iterator_traits<int *>::difference_type' (aka 'int') and 'const uint32_t' (aka 'const unsigned int') [-Werror,-Wsign-compare]
                    return std::count(subs.begin(), subs.end(), true) >= node.k;
                           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~
test/miniscript_tests.cpp:346:34: note: in instantiation of function template specialization 'miniscript::Node<CPubKey>::IsSatisfiable<(lambda at test/miniscript_tests.cpp:346:48)>' requested here
        bool satisfiable = node->IsSatisfiable([](const Node&) { return true; });
                                 ^
1 error generated.
```

cc @darosior 
{
        
        return TreeEval<int>([&fn](const Node& node, Span<int> subs) -> bool {
            switch (node.fragment) {
                case Fragment::JUST_0:
                    return false;
                case Fragment::JUST_1:
                    return true;
                case Fragment::PK_K:
                case Fragment::PK_H:
                case Fragment::MULTI:
                case Fragment::AFTER:
                case Fragment::OLDER:
                case Fragment::HASH256:
                case Fragment::HASH160:
                case Fragment::SHA256:
                case Fragment::RIPEMD160:
                    return bool{fn(node)};
                case Fragment::ANDOR:
                    return (subs[0] && subs[1]) || subs[2];
                case Fragment::AND_V:
                case Fragment::AND_B:
                    return subs[0] && subs[1];
                case Fragment::OR_B: