Update dependency net-imap to v0.5.4 (#2443)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

Gemfile.lock

@@ -280,7 +280,7 @@ GEM
     multi_xml (0.6.0)
     net-http (0.5.0)
       uri
-    net-imap (0.5.3)
+    net-imap (0.5.4)
       date
       net-protocol
     net-pop (0.1.2)