Bump Requires at least to 6.8

Author: mukeshpanchal27

plugins/auto-sizes/auto-sizes.php

@@ -3,7 +3,7 @@
  * Plugin Name: Enhanced Responsive Images
  * Plugin URI: https://github.com/WordPress/performance/tree/trunk/plugins/auto-sizes
  * Description: Improves responsive images with better sizes calculations and auto-sizes for lazy-loaded images.
- * Requires at least: 6.6
+ * Requires at least: 6.8
  * Requires PHP: 7.2
  * Version: 1.4.0
  * Author: WordPress Performance Team