fix: update build mode check to only consider child compilers' watching state

Author: bjohansebas

lib/Server.js

@@ -3629,8 +3629,7 @@ class Server {
     // `listen()` so the build can finish and the process can exit normally —
     // the user is not in control of the plugin lifecycle here, so we stay
     // silent rather than logging a warning.
-    const isBuildMode = () =>
-      childCompilers.every((child) => !child.watching && !child.options.watch);
+    const isBuildMode = () => childCompilers.every((child) => !child.watching);
 
     /**
      * @returns {Promise<void>} promise