Fix device class repairs issues placeholders in Group

[silamon]

Proposed change

Fixes home-assistant/frontend#19759

If possible, please add this to the next bugfix release.

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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 (group) you are listed as a code owner for? Thanks!

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[bouwew]

A good fix!

[MartinHjelmare]

Thanks!

Side note: I noticed that the description for the incorrect state class message starts with saying "device classes" instead of "state classes".

core/homeassistant/components/group/strings.json

Line 268 in 7c069a2

"description": "Device classes `{state_classes}` on source entities `{source_entities}` needs to be same for sensor group `{entity_id}`.\n\nPlease correct the state classes on the source entities and reload the group sensor to fix this issue."