[Backport 2.6] fix: struct_validator returns True instead of x to support empty arrays (#3182) (#3183)

Backport of #3182 to `2.6`.

Signed-off-by: zhuwenxing <wenxing.zhu@zilliz.com>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: zhuwenxing <wenxing.zhu@zilliz.com>
Co-authored-by: XuanYang-cn <xuan.yang@zilliz.com>

Author: 3 people

pymilvus/bulk_writer/validators.py

@@ -181,4 +181,4 @@ def struct_validator(x: object, max_cap: int):
     for k in x:
         if not isinstance(k, dict):
             raise MilvusException(message="only accept list of dict for STRUCT type field")
-    return x
+    return True