CI: ubuntu-rolling: fix configuration for sources after format change

```
# Ubuntu sources have moved to the /etc/apt/sources.list.d/ubuntu.sources
# file, which uses the deb822 format. Use deb822-formatted .sources files
# to manage package sources in the /etc/apt/sources.list.d/ directory.
# See the sources.list(5) manual page for details.
```

Adapt to the new format.

ci/ciimage/ubuntu-rolling/install.sh

@@ -29,7 +29,7 @@ pkgs=(
   openjdk-11-jre
 )
 
-sed -i '/^#\sdeb-src /s/^#//' "/etc/apt/sources.list"
+sed -i '/^Types: deb/s/deb/deb deb-src/' /etc/apt/sources.list.d/ubuntu.sources
 apt-get -y update
 apt-get -y upgrade
 apt-get -y install eatmydata