tls: improve debugging assertion

Refs: nodejs#22618

Author: addaleax

lib/_tls_wrap.js

@@ -64,7 +64,8 @@ function onhandshakestart(now) {
   debug('onhandshakestart');
 
   const { lastHandshakeTime } = this;
-  assert(now >= lastHandshakeTime);
+  assert(now >= lastHandshakeTime,
+         `now (${now}) < lastHandshakeTime (${lastHandshakeTime})`);
 
   this.lastHandshakeTime = now;