Temporarily disable automatic dark scheme

[alizedebray]

Dark scheme has been defined out-of-scope for v10.0.0, we therefore need to disable it temporarily.

To do:

• set the main color-scheme to light instead of light dark here:

  design-system/packages/styles/src/tokens/_schemes-static.scss

  Line 13 in 36f38ac

  color-scheme: light dark;

• check that dark scheme is not set when changing user's setting to prefer dark scheme
• check that dark scheme is still set when using the data-color-scheme="dark" attribute
• check the fallback solution in browsers that do not support light-dark()

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[...] since dark mode is out-of-scope for v10.0.0 can't we just set color-scheme: light; on the body for the moment and add back the color-scheme: light dark; only once the dark mode is ready?
(We would still be able to see the dark mode with data-color-scheme="dark" but the app would no longer react to the user settings)

Originally posted by @alizedebray in #6118