Manual test suite: there are probably multiple Received headers (refs: #16240).

wiki/src/contribute/release_process/test.mdwn

@@ -151,7 +151,7 @@ tracked by tickets prefixed with `todo/test_suite:`.
      SMTP relay that writes the IP address of the client it is
      relaying email for in the Received header).
   1. Then check that email's headers once received, especially the
-     `Received:` one.
+     `Received:` ones.
 * Also check that the EHLO/HELO SMTP message is not leaking anything
   at the application level:
   1. Start Thunderbird using the GNOME Applications menu.