Fix escape character in regex for Python 3.12+

[jackwillis]

I get this message when I run the script using Python 3.12 or greater:

/Users/jwillis/Code/onedrive_user_enum/./onedrive_enum.py:649: SyntaxWarning: invalid escape sequence '\/'
  domain_extract = re.findall('<Domain>(.*?)<\/Domain>', r.content.decode('utf-8'))

I adjusted the code to fix the escape characters in that regular expression. The backslash doesn't need to be escaped there.