Fix: Multiple block warning min height. (#8006)

The min-height style, for multiple block warnings, was not correct and the design was not right. The dimensions were updated.

edit-post/hooks/validate-multiple-use/index.js

@@ -69,7 +69,7 @@ const withMultipleValidation = createHigherOrderComponent( ( BlockEdit ) => {
 		const outboundType = getOutboundType( props.name );
 
 		return [
-			<div key="invalid-preview" style={ { minHeight: '100px' } }>
+			<div key="invalid-preview" style={ { minHeight: '60px' } }>
 				<BlockEdit key="block-edit" { ...props } />
 			</div>,
 			<Warning