Allow liter for gas sensor device class

[Arnie97]

Proposed change

Haier water heaters report their gas usage in liters,
so the corresponding custom integration produces WARNING logs like:

WARNING (Dummy-1) [homeassistant.components.sensor] Entity sensor.a08222a4c94c_totalusegasl (<class 'custom_components.haier.sensor.HaierSensor'>) is using native unit of measurement 'L' which is not a valid unit for the device class ('gas') it is using; expected one of ['m³', 'ft³', 'CCF']; Please update your configuration if your entity is manually configured, otherwise create a bug report at https://github.com/banto6/haier/issues

This patch fix the warning by allowing liter L as a valid unit for the gas sensor device class.

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)
• Deprecation (breaking change to happen in the future)
• 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 有一个单位兼容警告 banto6/haier#205
• This PR is related to issue: N/A
• Link to documentation pull request: Allow liter for gas sensor device class home-assistant.io#38221
• Link to developer documentation pull request: N/A
• Link to frontend pull request: N/A

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[home-assistant]

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

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

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[abmantis]

We also need to update the valid gas units on the energy sensor for the energy dashboard in homeassistant/components/energy/sensor.py.

[Arnie97]

Fixed the energy dashboard, please review again

[abmantis]

I would like to have a second opinion on this, since it will now do a conversion in cases where it didn't before.

[emontnemery]

The problem is that we allow gas to be measured either in a volume or as energy, so I don't think this will work (that's what the comment is trying to say).
It should be possible to do some rewrite, but that should happen in a separate PR, not in a PR adding support for liters.