auto-update: Link to the current release's changelog, not the latest one (#3076)

An user complained in zed-industries/community#2093 that we always link
to the latest release changelog, not the one that they've just updated
to.


Release Notes:
- Fixed changelog link in update notification always leading to the
latest release changelog, not the one that was updated to. Fixes
zed-industries/community#2093.