refactor: change conversion button content color

[GaspardMathon]

Describe the solution you'd like

• For the conversion variant button, we need to change the contentPrimary color to contentAccent color

Additional context

• Figma : https://www.figma.com/file/cmZCNVet64UlDNnDDd4hDV/Vitamin---iOS-14-UI-kit-(v0)?node-id=315%3A4517

[daniel-dumortier]

@GaspardMathon I think this issue is not relevant, because that is already the case in the latest release (which is the first on this repo) :

extension VitaminButton.Style {
    var foregroundColor: UIColor {
        switch self {
        case .primary:
            return VitaminColor.Core.Content.primaryReversed
        case .primaryReversed:
            return VitaminColor.Core.Content.primary
        case .secondary, .tertiary:
            return VitaminColor.Core.Content.action
        case .conversion:
            return VitaminColor.Core.Content.accent
        case .ghost:
            return VitaminColor.Core.Content.active
        case .ghostReversed:
            return VitaminColor.Core.Content.actionReversed
        }
    }
}

[lauthieb]

Nice! Thanks @daniel-dumortier