New stable branch (krita/5.3) for docs.krita.org

[Wolthera]

Hi,

We've just finished documenting the changes for Krita 5.3, and made a
new branch for it (krita/5.3).

Now, I am slightly lost because since last time, the website is using
gitlab CI, but as far as I know, we still need to manually update
Scripty to switch stable branches. My apologies if I got this wrong.

I have also held off on the sysadmin request to switch the website
upload to this new branch, as last time translations broke. So this
time, it would be good if we can double check things work and then I
can open a request to properly switch the website uploading.

Thanks in advance,

-- 
Wolthera