fix(assets): replace() use save/restore for Content-Type header

_api_client._call_request merges self.headers into every request via
headers.update(self.headers), which overwrites any per-request copy
before the request is sent. The only effective way to suppress
Content-Type for multipart uploads is to temporarily pop it from the
shared dict and restore it in a finally block.

Also retains the with-open() fix so the file handle is always closed
after the request.

Author: aniket-shikhare-cstk

contentstack_management/assets/assets.py

@@ -174,11 +174,17 @@ def replace(self, file_path):
         """
 
         url = f"assets/{self.asset_uid}"
-        # Omit Content-Type so requests can set it with the correct multipart boundary.
-        # Use a per-request header copy to avoid mutating the shared client headers dict.
-        request_headers = {k: v for k, v in self.client.headers.items() if k.lower() != "content-type"}
-        with open(file_path, 'rb') as fh:
-            return self.client.put(url, headers=request_headers, params=self.params, files={"asset": fh})
+        # _api_client._call_request does headers.update(self.headers) so a per-request
+        # copy is overwritten before the request is sent. The only way to suppress
+        # Content-Type is to temporarily remove it from the shared dict so requests can
+        # set multipart/form-data with the correct boundary automatically.
+        saved_ct = self.client.headers.pop("Content-Type", None)
+        try:
+            with open(file_path, 'rb') as fh:
+                return self.client.put(url, headers=self.client.headers, params=self.params, files={"asset": fh})
+        finally:
+            if saved_ct is not None:
+                self.client.headers["Content-Type"] = saved_ct
 
     def generate(self, data):
         """