feat: Error toast for "Not creating securejoin QR for old broadcast"

[iequidoo]

Follow-up to #7399 (see #7399 (comment)), otherwise the info message may not be visible enough

[Hocuri]

Thanks for following up!

At least on Android, the QR code isn't actually shown unfortunately - probably it was decided that error!() is being used too frequently, and that the error toasts do more harm than good.

We should at some point in the future discuss about that discrepancy between core expectations and UI behavior - maybe the UI can just start showing toasts again, or maybe it helps to create a new macro show_error_toast!() with a corresponding event. Not right now, probably, there are a lot of discussions already.