fix: add error cause to connectivity view for IMAP errors

For SMTP errors we already format `last_send_error` with {:#},
but for IMAP errors we have formatted the errors with .to_string().
This resulted in errors such as
"Error: IMAP failed to connect to example.org:443:tls"
instead of
"Error: IMAP failed to connect to example.org:443:tls: Connection failure: Network is unreachable (os error 101)."
in the connectivity view HTML.

src/imap.rs

@@ -489,7 +489,7 @@ impl Imap {
         let session = match self.connect(context, configuring).await {
             Ok(session) => session,
             Err(err) => {
-                self.connectivity.set_err(context, &err);
+                self.connectivity.set_err(context, format!("{err:#}"));
                 return Err(err);
             }
         };