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.
{
    fs::path settings = GetPathArg("-settings", fs::path{BITCOIN_SETTINGS_FILENAME});
    if (settings.empty()) {
        return false;
    }
    if (filepath) {
        *filepath = fsbridge::AbsPathJoin(GetDataDirNet(), temp ? settings + ".tmp" : settings);
    }
    return true;
}
static void SaveErrors(const std::vector<std::string> errors, std::vector<std::string>* error_out)
{
    for (const auto& error : errors) {
        if (error_out) {
            error_out->emplace_back(error);
        } else {
            LogPrintf("%s\n", error);
        }
    }
}
bool ArgsManager::ReadSettingsFile(std::vector<std::string>* errors)