Upgrade net-imap to 0.5.6 (#17078)

Author: mashhurs

Gemfile.jruby-3.1.lock.release

@@ -729,7 +729,7 @@ GEM
     mustermann (3.0.3)
       ruby2_keywords (~> 0.0.1)
     naught (1.1.0)
-    net-imap (0.5.5)
+    net-imap (0.5.6)
       date
       net-protocol
     net-pop (0.1.2)