www: use the in-tree release-notes, tarballs branch

Currently we copy the release notes to the website branch, only to copy them back again to public.

Stop that - just use one we already have.

With this the website branch contains only tarballs and their respective signature/checksums, so rename it to "tarballs".

Update the CI to handle the above, while also fixing the changes logic.

Signed-off-by: Emil Velikov emil.velikov@collabora.com