Improve backup websocket API tests

[emontnemery]

Proposed change

Improve backup websocket API tests by adding parametrized test cases for remote agents

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• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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• This PR fixes or closes issue: fixes #
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[home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (backup) you are listed as a code owner for? Thanks!

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[MartinHjelmare]

It would be better to patch some function that returns the backups that are then cached. Before this change we could have patched _read_backups to achieve this.

[emontnemery]

OK, let's consider that in a follow-up