test: increase limit for network space overhead test

This test imposes a limit on the average bytes of space per chunk
for network traffic. However this number depends on VM
implementation details, and upcoming changes to V8's
array buffer management require a small bump to this
limit in this test.

PR-URL: #28492
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/sequential/test-net-bytes-per-incoming-chunk-overhead.js

@@ -37,5 +37,5 @@ process.on('exit', () => {
   const bytesPerChunk =
     (process.memoryUsage().rss - baseRSS) / receivedChunks.length;
   // We should always have less than one page (usually ~ 4 kB) per chunk.
-  assert(bytesPerChunk < 512, `measured ${bytesPerChunk} bytes per chunk`);
+  assert(bytesPerChunk < 600, `measured ${bytesPerChunk} bytes per chunk`);
 });