* Migrate issue registry to use singleton helper
The other registries were already migrated, but since this
one had a read only flag, it required a slightly different
solution since it uses the same hass.data key
* refactor
* Don't blow up if validators can't access the issue registry
* Make the check_config script open issue_registry read only
* Update tests/helpers/test_issue_registry.py
Co-authored-by: Martin Hjelmare <marhje52@gmail.com>
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Co-authored-by: Martin Hjelmare <marhje52@gmail.com>
