Fix "set" / "sets" in action names and descriptions, spelling of "dB"

[NoRi2909]

Proposed change

The set_low_hz and set_sub_db actions of the KEF integration have "set" and "sets" swapped between the action name and its description. All other actions have this correct so it's inconsistent, too.

In addition this fixes the spelling of "dB" which has to keep the lowercase "d" SI prefix for "Dezi" in "Dezibel".

Type of change

• Dependency upgrade
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• Breaking change (fix/feature causing existing functionality to break)
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• This PR fixes or closes issue: fixes #
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[home-assistant]

Hey there @basnijholt, mind taking a look at this pull request as it has been labeled with an integration (kef) you are listed as a code owner for? Thanks!

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