fix(webpack): build in dev mode even when dev server's port is used

{{ cookiecutter.project_slug }}/webpack/webpack.config.js

@@ -56,6 +56,7 @@
 
 module.exports = function (_, argv) {
   const isDevelopment = argv.mode === "development";
+  const isServed = argv.env.WEBPACK_SERVE;
   const isProduction = argv.mode === "production";
   const port = process.env.PORT || 8080;
 
@@ -203,7 +204,7 @@
           },
         ],
       }),
-      isDevelopment && new CheckPortPlugin(port),
+      isServed && new CheckPortPlugin(port),
       isProduction && new BuildFolderWiper(buildDir),
       new webpack.DefinePlugin({
         "process.env.NODE_ENV": JSON.stringify(argv.mode),