assistant: mark "Accept" button as suggested action

38578054 added this style class to the "Next" button, and removed code that would set this class depending on whether the widget is sensitive. At the time I overlooked that the suggested-action style class should also be present for the "Accept" button on the EULA page: I think it's correct to say that accepting the EULA is the suggested action.

There is a third button which may appear in this position: "Skip". This is used (for example) on the Wi-Fi configuration page when no network is selected. It's correct not to mark this button as suggested: the suggested action is to configure a Wi-Fi network.

Before/After shots with Endless's custom EULA page (but this template is common):

(One screenshot was taken in a development container and one was taken on the host system – I guess they must have different fonts!)