Adds `multi_select` and `true_false` options to `CustomProperty.value_type` (#3173)

Adds `multi_select` and `true_false` options for `value_type` parameter
when creating custom properties.

See:
https://docs.github.com/en/rest/orgs/custom-properties?apiVersion=2022-11-28#create-or-update-custom-properties-for-an-organization

Fixes #3172

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Co-authored-by: Enrico Minack <github@enrico.minack.dev>