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.
assert(util::SettingsSpan(*includes).last_negated());
                use_conf_file = false;
            }
        }
        if (use_conf_file) {
            std::string chain_id = GetChainName();
            std::vector<std::string> conf_file_names;
            auto add_includes = [&](const std::string& network, size_t skip = 0) {
                size_t num_values = 0;
                LOCK(cs_args);
                if (auto* section = util::FindKey(m_settings.ro_config, network)) {
                    if (auto* values = util::FindKey(*section, "includeconf")) {
                        for (size_t i = std::max(skip, util::SettingsSpan(*values).negated()); i < values->size(); ++i) {
                            conf_file_names.push_back((*values)[i].get_str());
                        }
                        num_values = values->size();
                    }
                }
                return num_values;
            };
            
            
            const size_t chain_includes = add_includes(chain_id);
            const size_t default_includes = add_includes({});
            for (const std::string& conf_file_name : conf_file_names) {
                std::ifstream conf_file_stream{GetConfigFile(conf_file_name)};
                if (conf_file_stream.good()) {
                    if (!ReadConfigStream(conf_file_stream, conf_file_name, error, ignore_invalid_keys)) {
                        return false;