Add the ability to set the value of `prefers-colour-scheme`

[nicholasgriffintn]

Summary

prefers-colour-scheme is a feature that allows the user to switch between dark and light modes through a device level setting.

It would be fantastic if we could set the value of this setting so that we could test the colour contrast between the two modes.

I believe we will need to upgrade Electron in order to complete this.

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[github-actions]

This issue was closed because it has been stalled for 5 days with no activity.