Make parse_mode always lowercase (#575)

* Make parse_mode always lowercase

* Update client.py

Co-authored-by: Dan <14043624+delivrance@users.noreply.github.com>

pyrogram/client.py

@@ -397,6 +397,9 @@ class Client(Methods, Scaffold):
 
     @parse_mode.setter
     def parse_mode(self, parse_mode: Optional[str] = "combined"):
+        if isinstance(parse_mode, str):
+            parse_mode = parse_mode.lower()
+
         if parse_mode not in self.PARSE_MODES:
             raise ValueError('parse_mode must be one of {} or None. Not "{}"'.format(
                 ", ".join(f'"{m}"' for m in self.PARSE_MODES[:-1]),