vm,lib: refactor microtaskQueue assignment logic

Simplify the assignment of the `microtaskQueue` variable in the `vm`
module by replacing the conditional block with a more concise ternary
operator. This change improves code readability and maintainability.

PR-URL: #47765
Reviewed-By: theanarkh <theratliter@gmail.com>
Reviewed-By: Mestery <mestery@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/vm.js

@@ -236,14 +236,12 @@ function createContext(contextObject = {}, options = kEmptyObject) {
     validateBoolean(wasm, 'options.codeGeneration.wasm');
   }
 
-  let microtaskQueue = null;
-  if (microtaskMode !== undefined) {
-    validateOneOf(microtaskMode, 'options.microtaskMode',
-                  ['afterEvaluate', undefined]);
-
-    if (microtaskMode === 'afterEvaluate')
-      microtaskQueue = new MicrotaskQueue();
-  }
+  validateOneOf(microtaskMode,
+                'options.microtaskMode',
+                ['afterEvaluate', undefined]);
+  const microtaskQueue = microtaskMode === 'afterEvaluate' ?
+    new MicrotaskQueue() :
+    null;
 
   makeContext(contextObject, name, origin, strings, wasm, microtaskQueue);
   return contextObject;