[1.25] Collapse request chunked data and framing into one send() call (…

…urllib3#1906)

src/urllib3/connection.py

@@ -225,10 +225,11 @@ def request_chunked(self, method, url, body=None, headers=None):
                 if not isinstance(chunk, bytes):
                     chunk = chunk.encode("utf8")
                 len_str = hex(len(chunk))[2:]
-                self.send(len_str.encode("utf-8"))
-                self.send(b"\r\n")
-                self.send(chunk)
-                self.send(b"\r\n")
+                to_send = bytearray(len_str.encode())
+                to_send += b"\r\n"
+                to_send += chunk
+                to_send += b"\r\n"
+                self.send(to_send)
 
         # After the if clause, to always have a closed body
         self.send(b"0\r\n\r\n")