Enhance super_len to count encoded bytes for str

This is a possible fix for issue #6586

Author: bruceadams

src/requests/utils.py

@@ -134,7 +134,10 @@ def super_len(o):
     total_length = None
     current_position = 0
 
-    if hasattr(o, "__len__"):
+    if isinstance(o, str):
+        total_length = len(o.encode("utf-8"))
+
+    elif hasattr(o, "__len__"):
         total_length = len(o)
 
     elif hasattr(o, "len"):