Update tested version to 6.9 in readme

Author: vytisbulkevicius

readme.txt

@@ -2,7 +2,7 @@
 Contributors: codeinwp,marius2012,marius_codeinwp,hardeepasrani,Madalin_Themeisle, rsocial, uriahs-victor
 Tags: social media automation, auto post, social media scheduling, social media automation, social media sharing
 Requires at least: 4.7
-Tested up to: 6.8
+Tested up to: 6.9
 Requires PHP: 7.4
 Stable tag: trunk