Add test-before-setup rule to quality_scale validation

[epenet]

Proposed change

Spotted in #132227
Documented in https://developers.home-assistant.io/docs/core/integration-quality-scale/rules/test-before-setup/

Needs:

• Mark test-before-setup as exempt in mqtt #132334

Integrations: 1304
Invalid integrations: 1

Found errors. Generating files canceled.

Integration mqtt:
* [ERROR] [QUALITY_SCALE] [test-before-setup] Integration does not raise one of {'ConfigEntryAuthFailed', 'ConfigEntryNotReady', 'ConfigEntryError'} in async_setup_entry (homeassistant/components/mqtt/__init__.py)
* [ERROR] [QUALITY_SCALE] Please check the documentation at https://developers.home-assistant.io/docs/core/integration-quality-scale/rules/test-before-setup/

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 #
• This PR is related to issue:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[home-assistant]

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

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[jbouwh]

Okay for MQTT,
Thanks @epenet 👍