fix: push ws messages to array (#4513)

Author: kobenguyent

lib/helper/Playwright.js

@@ -3435,7 +3435,7 @@ class Playwright extends Helper {
   }
 
   _logWebsocketMessages(message) {
-    this.webSocketMessages += message
+    this.webSocketMessages.push(message)
   }
 }
 

lib/helper/Puppeteer.js

@@ -2772,7 +2772,7 @@ class Puppeteer extends Helper {
   }
 
   _logWebsocketMessages(message) {
-    this.webSocketMessages += message
+    this.webSocketMessages.push(message)
   }
 }