fix: Typo in key backup requests

This may lead to messages not decrypting after interactive verification,
which would make the user manually press the request keys button.

lib/encryption/key_manager.dart

@@ -66,7 +66,7 @@ class KeyManager {
             lastEvent.content['can_request_session'] == true) {
           try {
             maybeAutoRequest(room.id, lastEvent.content['session_id'],
-                lastEvent.content['sener_key']);
+                lastEvent.content['sender_key']);
           } catch (_) {
             // dispose
           }