add unknwon operation

Author: denrase

supabase/lib/src/operation.dart

@@ -3,7 +3,8 @@ enum Operation {
   insert('insert'),
   upsert('upsert'),
   update('update'),
-  delete('delete');
+  delete('delete'),
+  unknown('unknown');
 
   final String value;
   const Operation(this.value);

supabase/lib/src/sentry_supabase_request.dart

@@ -54,7 +54,7 @@ class SentrySupabaseRequest {
       case 'DELETE':
         return Operation.delete;
       default:
-        return Operation.select; // Should never happen.
+        return Operation.unknown; // Should never happen.
     }
   }