fix mypy

Signed-off-by: YunLiu <[email protected]>

Author: KumoLiu

monai/inferers/merger.py

@@ -247,6 +247,7 @@ def __init__(
         self.value_dtype = value_dtype
         self.count_dtype = count_dtype
         self.store = store
+        self.tmpdir: TemporaryDirectory | None
         if version_geq(get_package_version("zarr"), "3.0.0"):
             if value_store is None:
                 self.tmpdir = TemporaryDirectory()