Fix batch=-1 for exports (#3217)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

ultralytics/yolo/engine/model.py

@@ -335,7 +335,7 @@ class YOLO:
         overrides['mode'] = 'export'
         if overrides.get('imgsz') is None:
             overrides['imgsz'] = self.model.args['imgsz']  # use trained imgsz unless custom value is passed
-        if overrides.get('batch') is None:
+        if 'batch' not in kwargs:
             overrides['batch'] = 1  # default to 1 if not modified
         args = get_cfg(cfg=DEFAULT_CFG, overrides=overrides)
         args.task = self.task