Fix group entity availability handling

[dmulcahey]

fixes: https://github.com/home-assistant/core/issues/123518#issuecomment-2284411430

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.68%. Comparing base (6a3a2e4) to head (2bec1dd). Report is 1 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #164 +/- ## ======================================= Coverage 95.68% 95.68% ======================================= Files 61 61 Lines 9276 9276 ======================================= Hits 8876 8876 Misses 400 400 ```

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[dmulcahey]

gonna clean up the tests some more

[dmulcahey]

done