Get werkzeug version using importlib

[Sparrow0hawk]

Resolves deprecation warning:

.venv/lib/python3.11/site-packages/authlib/integrations/flask_oauth2/errors.py:4: DeprecationWarning: The '__version__' attribute is deprecated and will be removed in Werkzeug 3.1. Use feature detection or 'importlib.metadata.version("werkzeug")' instead.
    _version = werkzeug.__version__.split('.')[0]

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What kind of change does this PR introduce? (check at least one)

• [x] Bugfix
• [ ] Feature
• [ ] Code style update
• [ ] Refactor
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe the impact and migration path for existing applications:

(If no, please delete the above question and this text message.)

---

• [x] You consent that the copyright of your pull request source code belongs to Authlib's author.

[lepture]

@Sparrow0hawk tests failed.

[Sparrow0hawk]

@lepture please retry, should be fixed.

[azmeuk]

@lepture could there be a 1.2.2 hotfix for this? As the deprecation warning is emitted at the module level, the simple presence of authlib makes it noisy.

[lepture]

@azmeuk 1.3.0 released

[azmeuk]

Thank you @lepture Did you publish it on pypi? I cannot see 1.3 yet. https://pypi.org/project/Authlib/#history

[lepture]

@azmeuk published on pypi