Update Plex connection class to push

[jjlawren]

Proposed change

Sets the appropriate CONNECTION_CLASS to "local push" instead of "local poll".

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)
• 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 #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• Untested files have been added to .coveragerc.

The integration reached or maintains the following Integration Quality Scale:

• No score or internal
• 🥈 Silver
• 🥇 Gold
• 🏆 Platinum

[codecov]

Codecov Report

Merging #31806 into dev will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev   #31806   +/-   ##
=======================================
  Coverage   94.66%   94.67%           
=======================================
  Files         763      763           
  Lines       55114    55148   +34     
=======================================
+ Hits        52176    52212   +36     
+ Misses       2938     2936    -2     

Impacted Files	Coverage Δ
homeassistant/components/template/cover.py	96.34% <0.00%> (-1.37%)	⬇️
homeassistant/helpers/config_validation.py	95.66% <0.00%> (-0.40%)	⬇️
homeassistant/components/ps4/media_player.py	89.76% <0.00%> (-0.16%)	⬇️
homeassistant/components/teksavvy/sensor.py	97.77% <0.00%> (-0.03%)	⬇️
homeassistant/components/startca/sensor.py	97.95% <0.00%> (-0.03%)	⬇️
homeassistant/components/wled/const.py	100.00% <0.00%> (ø)	⬆️
homeassistant/components/fido/sensor.py	100.00% <0.00%> (ø)	⬆️
homeassistant/components/wled/sensor.py	100.00% <0.00%> (ø)	⬆️
homeassistant/components/simplisafe/const.py	100.00% <0.00%> (ø)	⬆️
homeassistant/components/unifi/controller.py	94.94% <0.00%> (+0.05%)	⬆️
... and 7 more

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