In preparation to removal of linux-postmarketos repo, switch
source to different source mirror.
P.S: sourcehut can't serve bz2 archives, I had to switch to gz
P.P.S: I'm not sure I'll keep repo on sourcehut forever, but let's try
See also: https://gitlab.com/postmarketOS/postmarketos/-/issues/47
[ci:skip-vercheck]
[ci:skip-build] Already built fine on CI in MR