chore(deps): bump net-imap to 0.6.4

    Patches GHSA-hm49-wcqc-g2xg (command injection via raw
    arguments) and GHSA-75xq-5h9v-w6px (command injection via
    unvalidated Symbol inputs). Both surfaced in CI on the M6
    reconnect-card PR; bumping here to unblock that branch.

Author: bstruong

Gemfile.lock

@@ -158,7 +158,7 @@ GEM
       drb (~> 2.0)
       prism (~> 1.5)
     msgpack (1.8.0)
-    net-imap (0.6.3)
+    net-imap (0.6.4)
       date
       net-protocol
     net-pop (0.1.2)