Bump PlexAPI to 4.15.13

[jjlawren]

Proposed change

https://github.com/pkkid/python-plexapi/releases/tag/4.15.13
Full diff: pkkid/python-plexapi@4.15.12...4.15.13

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes Plex: SyntaxWarning: invalid escape sequence '\.' """ #114471
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
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• Tests have been added to verify that the new code works.

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