DKIM-Checking: Don't disallowing keychanges for now

To get back to a releaseable state - the info stays accessible in the
Message-info.

We can re-enable it as soon as it has been tested thoroughly.

src/decrypt.rs

@@ -79,7 +79,8 @@ pub async fn prepare_decryption(
         from,
         autocrypt_header.as_ref(),
         message_time,
-        dkim_results.allow_keychange,
+        // Disallowing keychanges is disabled for now:
+        true, // dkim_results.allow_keychange,
     )
     .await?;