benchmark: use smaller n value in some http tests

PR-URL: https://github.com/nodejs/node/pull/14002
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

benchmark/http/check_invalid_header_char.js

@@ -27,7 +27,7 @@ const bench = common.createBenchmark(main, {
     'foo\nbar',
     '\x7F'
   ],
-  n: [5e8],
+  n: [1e6],
 });
 
 function main(conf) {

benchmark/http/check_is_http_token.js

@@ -37,7 +37,7 @@ const bench = common.createBenchmark(main, {
     ':alternate-protocol', // fast bailout
     'alternate-protocol:' // slow bailout
   ],
-  n: [5e8],
+  n: [1e6],
 });
 
 function main(conf) {