Update the onboarding link for 12.0

A user found in the alpha that 12.0a5's onboarding is still pointing to 11.5 release notes.

Even though 12.0 notes do not exist yet, we should update the link to make it sure the correct one appears in 12.0.

added Doing label

assigned to @pierov

mentioned in merge request !471 (merged)

closed

removed Doing label

marked this issue as related to tor-browser-build#40637 (closed)