Fix pasting plain text

Author: mkaz

src/edit.js

@@ -185,6 +185,7 @@ const edit = ( { attributes, className, setAttributes } ) => {
 							preserveWhiteSpace={ true }
 							allowedFormats={ [] }
 							withoutInteractiveFormatting={ true }
+							__unstablePastePlainText={ true /* GB 9.5 */ }
 						/>
 					</pre>
 				) : useLightBlockWrapper ? (