reactions are not a 'probably private reply'

`is_probably_private_reply()` checks
if a message should better go to the one to one chat
instead of the chat already identified by the `In-Reply-To`.
this functionality is needed to make "Reply Privately" work.

however, this functionality is never true for reactions.
if we would return `true` here, own reactions seen by a second device
would not get the correct chat assiged.

src/receive_imf.rs

@@ -1721,6 +1721,11 @@ async fn is_probably_private_reply(
         }
     }
 
+    let is_reaction = mime_parser.parts.iter().any(|part| part.is_reaction);
+    if is_reaction {
+        return Ok(false);
+    }
+
     Ok(true)
 }