Support action YAML syntax in old-style notify groups

[frenck]

Proposed change

This one was missed in the services -> actions change: Old-style groups for notification services/actions.

fixes home-assistant/home-assistant.io#34223

TODO:

• Add test coverage

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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Additional information

• This PR fixes or closes issue: fixes typo in Notify groups? home-assistant.io#34223
• This PR is related to issue:
• Link to documentation pull request:

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