Change multi_select config validator to class

[Kane610]

Breaking change

Proposed change

Following discussion in #31798

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

Example entry for configuration.yaml:

# Example configuration.yaml

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue: Add multi select support to config validation and to custom serializer #31798
• 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.

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[balloob]

You need to update the serializer too, and please also add a test for the serializer.

[Kane610]

@balloob done

[codecov]

Codecov Report

Merging #31828 into dev will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev   #31828      +/-   ##
==========================================
+ Coverage   94.65%   94.66%   +<.01%     
==========================================
  Files         763      763              
  Lines       55160    55164       +4     
==========================================
+ Hits        52213    52221       +8     
+ Misses       2947     2943       -4

Impacted Files	Coverage Δ
homeassistant/helpers/config_validation.py	95.92% <100%> (+0.26%)	⬆️
...stant/components/homekit_controller/config_flow.py	100% <0%> (ø)	⬆️
homeassistant/components/coolmaster/config_flow.py	100% <0%> (ø)	⬆️
homeassistant/components/esphome/config_flow.py	100% <0%> (ø)	⬆️
homeassistant/helpers/restore_state.py	98.44% <0%> (+0.01%)	⬆️
homeassistant/helpers/entity_component.py	96.82% <0%> (+0.02%)	⬆️
homeassistant/components/template/cover.py	97.71% <0%> (+1.36%)	⬆️

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[jjlawren]

Very possible I'm missing something on my side, but I'm not able to get this work. Slightly different error from the comment in the previous case.

data_schema=vol.Schema(
    {
        vol.Optional("users"): cv.multi_select(
            {"user1": "user1", "user2": "user2"}
        ),
    }
)

  File "/home/homeassistant/src/home-assistant/venv/lib/python3.7/site-packages/voluptuous_serialize/__init__.py", line 108, in convert
    raise ValueError('Unable to convert schema: {}'.format(schema))
ValueError: Unable to convert schema: <homeassistant.helpers.config_validation.multi_select object at 0x7ff1b7771050>

[balloob]

Where are you serializing it? The serializer needs to reference the custom serializer to work.