test: update example to use manifest v3

Chromium does not allow v2 anymore, and was rejecting example extension.

Author: ahwayakchih

example/example-extension.crx

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <gupdate xmlns="http://www.google.com/update2/response" protocol="2.0">
   <app appid="oldmflkhpnhejcakhabdmkjafmccabek">
-    <updatecheck codebase="http://127.0.0.1:8080/example-extension.crx" version="1.0" prodversionmin="64.0.3242" />
+    <updatecheck codebase="http://127.0.0.1:8080/example-extension.crx" version="1.0" prodversionmin="126" />
   </app>
 </gupdate>

example/example-extension.xml

@@ -2,8 +2,8 @@
 	"name": "Example That Does Nothing",
 	"version": "1.0",
 	"description": "Create a better one!",
-	"manifest_version": 2,
-	"minimum_chrome_version": "60",
+	"manifest_version": 3,
+	"minimum_chrome_version": "126",
 	"content_scripts": [
 		{
 			"matches": ["http://127.0.0.1:8080/*"],