org: update link to dev tarball

* doc/org/install.org: Point to the gitlab-ci artefacts.
10 jobs for next in 238 minutes and 46 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build
passed arch-clang #1253

00:31:25

passed arch-gcc-glibcxxdebug #1254

00:40:12

passed debian-stable-gcc #1251

00:37:37

passed debian-unstable-gcc-coverage #1252

00:30:10

88.9%
passed debpkg-stable #1257

01:53:28

passed debpkg-unstable #1261

02:22:35

passed mingw-shared #1255

00:09:14

passed mingw-static #1256

00:09:05

failed debpkg-unstable #1258

00:00:39

 
  Publish
passed publish-unstable #1259
dput

00:02:42