Fix ELKM1 entity service schema

[frenck]

Proposed change

Fixes the entity service schema for the ELKM1 integration to ensure it works with service targets.

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.
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• Tests have been added to verify that the new code works.

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[probot-home-assistant]

Hey there @gwww, @bdraco, mind taking a look at this pull request as its been labeled with an integration (elkm1) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[gwww]

Looks ok to me. Did something actually break or is this to bring the code in line with another change... or something else?

Thanks!

[frenck]

@gwww In the previous format, it would break service calls that use the target format, using e.g., an area or device.