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.
{
    auto get_net = [&](const std::string& arg) {
        LOCK(cs_args);
        util::SettingsValue value = util::GetSetting(m_settings,  "", SettingName(arg),
             false,
             true);
        return value.isNull() ? false : value.isBool() ? value.get_bool() : InterpretBool(value.get_str());
    };
    const bool fRegTest = get_net("-regtest");
    const bool fSigNet  = get_net("-signet");
    const bool fTestNet = get_net("-testnet");
    const bool is_chain_arg_set = IsArgSet("-chain");
    if ((int)is_chain_arg_set + (int)fRegTest + (int)fSigNet + (int)fTestNet > 1) {
        throw std::runtime_error("Invalid combination of -regtest, -signet, -testnet and -chain. Can use at most one.");
    }
    if (fRegTest)
        return CBaseChainParams::REGTEST;
    if (fSigNet) {
        return CBaseChainParams::SIGNET;
    }
    if (fTestNet)
        return CBaseChainParams::TESTNET;
    return GetArg("-chain", CBaseChainParams::MAIN);
}
bool ArgsManager::UseDefaultSection(const std::string& arg) const