fix: acceptInvite deprecated

[mtthidoteu]

Description

MyPlexAccount.acceptInvite now targets Plex TV’s new v2 endpoint:

• Replaced the deprecated
  PUT https://plex.tv/api/invites/requests/{invite.id}
  with
  POST https://plex.tv/api/v2/shared_servers/{invite.id}/accept.

This keeps the library working after Plex removed the old route.

Fixes #1536

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature
• Breaking change
• 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 (existing tests that cover acceptInvite still pass)