Fix caching error when response didn't set Content-Type header

Author: gerrod3

pulp_container/app/cache.py

@@ -41,7 +41,8 @@ async def make_response(self, key, base_key):
         """Fix the Content-Type header to remove the charset."""
         response = await super().make_response(key, base_key)
         if response is not None:
-            response.headers["Content-Type"] = response.headers["Content-Type"].split(";")[0]
+            if content_type := response.headers.get("Content-Type"):
+                response.headers["Content-Type"] = content_type.split(";")[0]
         return response