Error: listen EADDRINUSE: address already in use :::8124

```
ruby/3.0.0/gems/jekyll-postcss-0.5.0/bin/postcss:31
throw err;
^

Error: listen EADDRINUSE: address already in use :::8124
at Server.setupListenHandle [as _listen2] (net.js:1331:16)
at listenInCluster (net.js:1379:12)
at Server.listen (net.js:1465:7)
at Function.startServer (/home/metapodcod/.gem/ruby/3.0.0/gems/jekyll-postcss-0.5.0/bin/postcss:34:12)
at Object. (/home/metapodcod/.gem/ruby/3.0.0/gems/jekyll-postcss-0.5.0/bin/postcss:42:13)
at Module._compile (internal/modules/cjs/loader.js:1085:14)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:1114:10)
at Module.load (internal/modules/cjs/loader.js:950:32)
at Function.Module._load (internal/modules/cjs/loader.js:790:12)
at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:76:12) {
code: 'EADDRINUSE',
errno: -98,
syscall: 'listen',
address: '::',
port: 8124
}
done in 1.044 seconds.
```

The stack trace points to jekyll-postcss-0.5.0/bin/postcss and the startServer entry point; begin by reading that entry point and reproducing startup on port 8124. Done means the reported Jekyll/PostCSS startup no longer fails with EADDRINUSE, but the issue does not specify the intended resolution or any tests.

Written by the indexing model from the issue text.