benchmark: fix http elapsed time

Since commit 4e9ad20, elapsed time is expected to be a BigInt
instead of an array.

Refs: nodejs#38369

benchmark/_http-benchmarkers.js

@@ -222,7 +222,7 @@ exports.run = function(options, callback) {
     return;
   }
 
-  const benchmarker_start = process.hrtime();
+  const benchmarker_start = process.hrtime.bigint();
 
   const child = benchmarker.create(options);
 
@@ -233,7 +233,7 @@ exports.run = function(options, callback) {
   child.stdout.on('data', (chunk) => stdout += chunk);
 
   child.once('close', (code) => {
-    const elapsed = process.hrtime(benchmarker_start);
+    const benchmark_end = process.hrtime.bigint();
     if (code) {
       let error_message = `${options.benchmarker} failed with ${code}.`;
       if (stdout !== '') {
@@ -250,6 +250,7 @@ exports.run = function(options, callback) {
       return;
     }
 
+    const elapsed = benchmark_end - benchmarker_start;
     callback(null, code, options.benchmarker, result, elapsed);
   });