test: add missing console.error to exec-maxBuffer

Adds the missing console.error to test-child-process-exec-maxBuffer

PR-URL: #14796
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: David Cai <davidcai1993@yahoo.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

test/parallel/test-child-process-exec-maxBuffer.js

@@ -25,7 +25,7 @@ const unicode = '中文测试'; // length = 4, byte length = 12
 }
 
 {
-  const cmd = `"${process.execPath}" -e "console.('${unicode}');"`;
+  const cmd = `"${process.execPath}" -e "console.error('${unicode}');"`;
 
   cp.exec(cmd, {maxBuffer: 10}, checkFactory('stderr'));
 }