debugger: revise async iterator usage to comply with lint rules

I'm not sure that this is any clearer than the existing code, but I
don't think it's significantly less clear, and it avoids comment
disabling a lint rule.

Author: Trott

lib/internal/inspector/_inspect.js

@@ -87,8 +87,8 @@ async function portIsFree(host, port, timeout = 9999) {
 
   setTimeout(timeout).then(() => ac.abort());
 
-  // eslint-disable-next-line no-unused-vars
-  for await (const _ of setInterval(retryDelay)) {
+  const asyncIterator = setInterval(retryDelay);
+  while (await asyncIterator.next()) {
     if (signal.aborted) {
       throw new StartupError(
         `Timeout (${timeout}) waiting for ${host}:${port} to be free`);