Tweak z-index for cover block internals

packages/base-styles/_z-index.scss

@@ -37,7 +37,7 @@ $z-layers: (
 	".edit-site-header": 62,
 	".edit-widgets-header": 30,
 	".block-library-button__inline-link .block-editor-url-input__suggestions": 6, // URL suggestions for button block above sibling inserter
-	".wp-block-cover__inner-container": 1, // InnerBlocks area inside cover image block
+	".wp-block-cover__inner-container": 32, // InnerBlocks area inside cover image block. Must be higher than block popover and less than drop zone.
 	".wp-block-cover.is-placeholder .components-placeholder.is-large": 1, // Cover block resizer component inside a large placeholder.
 	".wp-block-cover.has-background-dim::before": 1, // Overlay area inside block cover need to be higher than the video background.
 	".block-library-cover__padding-visualizer": 2, // BoxControl visualizer needs to be +1 higher than .wp-block-cover.has-background-dim::before