Update readme.txt

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Author: sy-records

readme.txt

@@ -3,7 +3,7 @@ Contributors: shenyanzhi
 Donate link: https://qq52o.me/sponsor.html
 Tags: COS, 腾讯云, 对象存储, Tencent, Qcloud
 Requires at least: 4.6
-Tested up to: 6.8
+Tested up to: 6.9
 Requires PHP: 7.2
 Stable tag: 2.6.6
 License: Apache2.0