Fix unpin hint on the pinned pull requests (#33207)

options/locale/locale_en-US.ini

@@ -1652,7 +1652,7 @@ issues.attachment.open_tab = `Click to see "%s" in a new tab`
 issues.attachment.download = `Click to download "%s"`
 issues.subscribe = Subscribe
 issues.unsubscribe = Unsubscribe
-issues.unpin_issue = Unpin Issue
+issues.unpin = Unpin
 issues.max_pinned = "You can't pin more issues"
 issues.pin_comment = "pinned this %s"
 issues.unpin_comment = "unpinned this %s"