Fix escape sequence in docstring regex

[jjlawren]

Description

py.warnings logs a warning when imported in some projects:

[py.warnings] /usr/local/lib/python3.12/site-packages/plexapi/base.py:174: SyntaxWarning: invalid escape sequence '\d' """ Load the specified key to find and build all items with the specified tag

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the docstring for new or existing methods
• I have added tests when applicable

[jjlawren]

This was partially fixed in #1370.