fix(python): with_content_type should resolve to specified file conte…

…nt type when provided.

generators/python/core_utilities/shared/file.py

@@ -48,13 +48,15 @@ def with_content_type(*, file: File, content_type: str) -> File:
             filename, content = cast(Tuple[Optional[str], FileContent], file)  # type: ignore
             return (filename, content, content_type)
         elif len(file) == 3:
-            filename, content, _ = cast(Tuple[Optional[str], FileContent, Optional[str]], file)  # type: ignore
-            return (filename, content, content_type)
+            filename, content, file_content_type = cast(Tuple[Optional[str], FileContent, Optional[str]], file)  # type: ignore
+            out_content_type = file_content_type or content_type
+            return (filename, content, out_content_type)
         elif len(file) == 4:
-            filename, content, _, headers = cast(  # type: ignore
+            filename, content, file_content_type, headers = cast(  # type: ignore
                 Tuple[Optional[str], FileContent, Optional[str], Mapping[str, str]], file
             )
-            return (filename, content, content_type, headers)
+            out_content_type = file_content_type or content_type
+            return (filename, content, out_content_type, headers)
         else:
             raise ValueError(f"Unexpected tuple length: {len(file)}")
     return (None, file, content_type)