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 
uint32_t m_flags;
    
    explicit constexpr Type(uint32_t flags) : m_flags(flags) {}
public:
    
    friend constexpr Type operator"" _mst(const char* c, size_t l);
    
    constexpr Type operator|(Type x) const { return Type(m_flags | x.m_flags); }
    
    constexpr Type operator&(Type x) const { return Type(m_flags & x.m_flags); }
    
    constexpr bool operator<<(Type x) const { return (x.m_flags & ~m_flags) == 0; }
    
    constexpr bool operator<(Type x) const { return m_flags < x.m_flags; }
    
    constexpr bool operator==(Type x) const { return m_flags == x.m_flags; }
    
    constexpr Type If(bool x) const { return Type(x ? m_flags : 0); }
};
inline constexpr Type operator"" _mst(const char* c, size_t l) {
    Type typ{0};
    for (const char *p = c; p < c + l; p++) {
        typ = typ | Type(