test: remove try/catch in common.isMainThread

Refactor common.isMainThread.

PR-URL: #25249
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/common/index.js

@@ -40,12 +40,11 @@ const noop = () => {};
 const hasCrypto = Boolean(process.versions.openssl);
 
 const isMainThread = (() => {
-  try {
+  if (require('module').builtinModules.includes('worker_threads')) {
     return require('worker_threads').isMainThread;
-  } catch {
-    // Worker module not enabled → only a single main thread exists.
-    return true;
   }
+  // Worker module not enabled → only a single main thread exists.
+  return true;
 })();
 
 // Check for flags. Skip this for workers (both, the `cluster` module and