Re-disable DKIM-checks (#4076)

src/decrypt.rs

@@ -99,7 +99,8 @@ pub(crate) 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?;