Add temporary package constraint on flexparser and pint to fix CI

[epenet]

Proposed change

flexparser 0.4 was released a few hours ago, which breaks pint.
https://pypi.org/project/flexparser/#history

See hgrecco/pint#1969

Sample CI failure:
https://github.com/home-assistant/core/actions/runs/11716301319/job/32634642240?pr=130005
https://github.com/home-assistant/core/actions/runs/11718640751/job/32640345287?pr=129963

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.
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• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.

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To help with the load of incoming pull requests:

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[cdce8p]

Let's pin both flexparser and pint to exact versions for now.

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

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[cdce8p]

Thanks @epenet 👍🏻

[emontnemery]

Thanks, @epenet 👍

[cdce8p]

Removed the milestone since pint 0.24.4 was released an hour ago. See #130070.