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);
    fs::path& path = net_specific ? m_cached_network_datadir_path : m_cached_datadir_path;
    
    
    if (!path.empty()) return path;
    const fs::path datadir{GetPathArg("-datadir")};
    if (!datadir.empty()) {
        path = fs::absolute(datadir);
        if (!fs::is_directory(path)) {
            path = "";
            return path;
        }
    } else {
        path = GetDefaultDataDir();
    }
    if (!fs::exists(path)) {
        fs::create_directories(path / "wallets");
    }
    if (net_specific && !BaseParams().DataDir().empty()) {
        path /= fs::PathFromString(BaseParams().DataDir());
        if (!fs::exists(path)) {
            fs::create_directories(path / "wallets");
        }
    }
    return path;
}
void ArgsManager::ClearPathCache()