Fix DeprecationWarning in escape_markdown()

Using `count` as positional argument to `re.sub` is deprecated since
Python 3.13.

Fixes #10490

discord/utils.py

@@ -1008,7 +1008,7 @@ def escape_markdown(text: str, *, as_needed: bool = False, ignore_links: bool =
         regex = _MARKDOWN_STOCK_REGEX
         if ignore_links:
             regex = f'(?:{_URL_REGEX}|{regex})'
-        return re.sub(regex, replacement, text, 0, re.MULTILINE)
+        return re.sub(regex, replacement, text, count=0, flags=re.MULTILINE)
     else:
         text = re.sub(r'\\', r'\\\\', text)
         return _MARKDOWN_ESCAPE_REGEX.sub(r'\\\1', text)