charmcraft: migrate to python@3.14

[daeho-ro]

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[github-actions]

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[chenrui333]

seeing some issue with 4.0.1 release build and downgrade it to use py3.13, #249934

  ==> /home/linuxbrew/.linuxbrew/Cellar/charmcraft/4.0.1/bin/charmcraft version
  /home/linuxbrew/.linuxbrew/Cellar/charmcraft/4.0.1/libexec/lib/python3.14/site-packages/charmcraft/models/project.py:33: UserWarning: Core Pydantic V1 functionality isn't compatible with Python 3.14 or greater.
    import pydantic.v1
  charmcraft internal error: PermissionError(13, 'Permission denied')