fix: Markdown component can emit console error "invalid dom nesting" with nested <p>

part of #7856

Author: starpit

plugins/plugin-client-common/src/components/Content/Markdown.tsx

@@ -149,7 +149,7 @@ export default class Markdown extends React.PureComponent<Props> {
                   .filter(_ => _)
                 return <React.Fragment>{imageTags}</React.Fragment>
               } else if (/^<br\s*\/?>$/.test(props.value)) {
-                return <p />
+                return <br />
               } else if (/<a name=/.test(props.value)) {
                 const nameMatch = props.value.match(/name="?([^"\s]+)"?/)
                 if (nameMatch) {