Block: change ‘edit as HTML’ text

Change the ‘edit as HTML’ button text for an invalid block so it better matches the action.

editor/components/block-list/block-invalid-warning.js

@@ -26,7 +26,7 @@ function BlockInvalidWarning( { convertToHTML, convertToBlocks } ) {
 				</Button>,
 				hasHTMLBlock && (
 					<Button key="edit" onClick={ convertToHTML } isLarge isPrimary>
-						{ __( 'Edit as HTML' ) }
+						{ __( 'Keep as HTML' ) }
 					</Button>
 				),
 			] }