chore: add log when exiting the sync loop's stream

Signed-off-by: Benjamin Bouvier <public@benj.me>

crates/matrix-sdk/src/sliding_sync/mod.rs

@@ -654,6 +654,8 @@ impl SlidingSync {
                     }
                 }
             }
+
+            debug!("Sync stream loop has exited.");
         }
     }