Test on macOS 12.2.1 against the master branch. #24397 doesn't fix it.

```
brew info boost
boost: stable 1.78.0 (bottled), HEAD
...
./configure --enable-external-signer
...
checking for boostlib >= 1.64.0 (106400)... yes
checking whether Boost.Process can be used... no
configure: error: External signing is not supported for this Boost version
```

It does work with boost 1.76 (there was no 1.77 release in home-brew):

```
brew install boost@1.76
...
LDFLAGS="-L/usr/local/opt/boost@1.76/lib" CPPFLAGS="-I/usr/local/opt/boost@1.76/include" ./configure --enable-external-signer
...
checking for boostlib >= 1.64.0 (106400)... yes
checking whether Boost.Process can be used... yes
...
Options used to compile and link:
  external signer = yes
```

There's nothing in the release notes about Boost.Process for either [1.77](https://www.boost.org/users/history/version_1_77_0.html) or [1.78](https://www.boost.org/users/history/version_1_78_0.html).

The Homebrew [formula changes](https://github.com/Homebrew/homebrew-core/commits/master/Formula/boost.rb) are nothing but a trivial version and hash bump.
{
    LOCK(cs_args);
    m_cached_datadir_path = fs::path();
    m_cached_network_datadir_path = fs::path();
    m_cached_blocks_path = fs::path();
}
std::optional<const ArgsManager::Command> ArgsManager::GetCommand() const
{
    Command ret;
    LOCK(cs_args);
    auto it = m_command.begin();
    if (it == m_command.end()) {
        
        return std::nullopt;
    }
    if (!m_accept_any_command) {
        
        ret.command = *(it++);
    }
    while (it != m_command.end()) {
        
        ret.args.push_back(*(it++));
    }
    return ret;
}
std::vector<std::string> ArgsManager::GetArgs(const std::string& strArg) const