test: correct header length subtraction

In test-http-max-http-headers, a comment asks why we are subtracting 32
from the length of the invalid-length-by-1 headers instead of just 1.
Subtracting 1 seems to be correct and works.

PR-URL: #30712
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: Trott

test/sequential/test-http-max-http-headers.js

@@ -37,8 +37,7 @@ function fillHeaders(headers, currentSize, valid = false) {
 
   // Generate valid headers
   if (valid) {
-    // TODO(mcollina): understand why -32 is needed instead of -1
-    headers = headers.slice(0, -32);
+    headers = headers.slice(0, -1);
   }
   return headers + '\r\n\r\n';
 }