Strip tags from og:description on public tag page (#7437)

app/views/tags/_og.html.haml

@@ -2,5 +2,5 @@
 = opengraph 'og:url', tag_url(@tag)
 = opengraph 'og:type', 'website'
 = opengraph 'og:title', "##{@tag.name}"
-= opengraph 'og:description', t('about.about_hashtag_html', hashtag: @tag.name)
+= opengraph 'og:description', strip_tags(t('about.about_hashtag_html', hashtag: @tag.name))
 = opengraph 'twitter:card', 'summary'