Fix tox extras=None validation

[hugovk]

tox 4.36.0 added extra validation:

• https://github.com/tox-dev/tox/releases/tag/4.36.0
• ✨ feat(package): validate extras against package metadata tox-dev/tox#3696

Which caused the pinned runs to fail:

Run uvx --with tox-uv tox -e pins
pins: venv> /home/runner/work/_temp/setup-uv-cache/archive-v0/WaN7jz0jfp6uKMzXDt3xR/bin/uv venv -p /home/runner/work/_temp/setup-uv-cache/archive-v0/WaN7jz0jfp6uKMzXDt3xR/bin/python --allow-existing '--prompt=norwegianblue[pins]' --python-preference system /home/runner/work/norwegianblue/norwegianblue/.tox/pins
pins: install_deps> /home/runner/work/_temp/setup-uv-cache/archive-v0/WaN7jz0jfp6uKMzXDt3xR/bin/uv pip install -r requirements.txt
pins: failed with extras not found for package norwegianblue: none (available: tests)
  pins: FAIL code 1 (0.17 seconds)
  evaluation failed :( (0.21 seconds)

https://github.com/hugovk/norwegianblue/actions/runs/22537249267/job/65286847724?pr=288

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.62%. Comparing base (158f72b) to head (7e3b6fd).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #289   +/-   ##
=======================================
  Coverage   98.62%   98.62%           
=======================================
  Files           7        7           
  Lines         437      437           
=======================================
  Hits          431      431           
  Misses          6        6           

Flag	Coverage Δ
macos-latest	98.62% <ø> (ø)
ubuntu-latest	98.62% <ø> (ø)
windows-latest	98.62% <ø> (ø)

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