Block List HOC: Ensure className is preserved (#14738)

As the HOC was used as part of a filter, the className was getting set
by the last filter that was run. This was a lucky accident for OpenTable
as it meant that it wasn't affected by the bug being fixed in #14732

This change passes through the className prop when the block names don't
match, which means that if it's been set by a previous filter, it is
preserved.

extensions/shared/with-has-warning-is-interactive-class-names/index.jsx

@@ -14,7 +14,7 @@ export default name =>
 		BlockListBlock => props => (
 			<BlockListBlock
 				{ ...props }
-				className={ props.name === name ? 'has-warning is-interactive' : '' }
+				className={ props.name === name ? 'has-warning is-interactive' : props.className }
 			/>
 		),
 		'withHasWarningIsInteractiveClassNames'