Use the new media query for dark theme for the "Connected" pill in bridges

For #41054 (closed) we fixed the color of the "Connected" pill of the bridge card.

However, we did it for 12.0a1, which was still on v91 and used a proprietary media query. We should switch to the new one.

I've also looked for other -moz-toolbar-prefers-color-scheme, but it seems this is the last one.