test_runner: refactor Promise chain in run()

This commit refactors the chain of functions in run() to use an
async function instead of creating an awkward primordial-based
Promise chain.

lib/internal/test_runner/runner.js

@@ -17,7 +17,6 @@ const {
   ArrayPrototypeSort,
   ObjectAssign,
   PromisePrototypeThen,
-  PromiseResolve,
   PromiseWithResolvers,
   SafeMap,
   SafePromiseAll,
@@ -801,9 +800,17 @@ function run(options = kEmptyObject) {
     }
   }
 
-  const setupPromise = PromiseResolve(setup?.(root.reporter));
-  PromisePrototypeThen(PromisePrototypeThen(PromisePrototypeThen(setupPromise, runFiles), postRun), teardown);
+  const runChain = async () => {
+    if (typeof setup === 'function') {
+      await setup(root.reporter);
+    }
+
+    await runFiles();
+    postRun?.();
+    teardown?.();
+  };
 
+  runChain();
   return root.reporter;
 }