Install git into Alpine CI image to fix autopoint error (!107)

Alpine Linux build CI job fails like this:
    $ ./autogen.sh
    ...
    Running autoreconf...
    autoreconf: export WARNINGS=no-portability
    autoreconf: Entering directory '.'
    autoreconf: running: autopoint --force
    autopoint: *** git program not found
    autopoint: *** Stop.
    autoreconf: error: autopoint failed with exit status: 1

This is because gettext's autopoint command in Alpine Linux is built
with a git archive of application support files:
    $ autopoint --version
    /usr/bin/autopoint (GNU gettext-tools) 0.21
    Uses a versions archive in git format.
    ...
    $ ls -l /usr/share/gettext/archive*
    -rw-r--r-- 1 root root 752320 Jan 14 2021 /usr/share/gettext/archive.git.tar.gz

Where as for other distributions gettext's autopoint command uses plain
compressed tar archive, for example in Ubuntu 22.04 LTS:
    $ autopoint --version
    /usr/bin/autopoint (GNU gettext-tools) 0.21
    Uses a versions archive in dirxz format.
    ...
    $ ls -l /usr/share/gettext/archive*
    -rw-r--r-- 1 root root 407064 Mar 25 10:31 /usr/share/gettext/archive.dir.tar.xz

Fix by adding git to the packages installed into the Alpine Linux CI
docker image.

Closes !107 - Migrate from intltool to gettext translation

.gitlab-ci.yml

@@ -10,7 +10,7 @@ stages:
     - cat /etc/os-release
     - apk update
     - apk add gnome-common yelp-tools automake autoconf glib-dev intltool
-              libtool g++ parted-dev gtkmm3-dev itstool make
+              libtool g++ parted-dev gtkmm3-dev itstool make git
     # Extra packages only needed during the test stage.
     - apk add btrfs-progs btrfs-progs-extra e2fsprogs e2fsprogs-extra exfatprogs
               dosfstools mtools f2fs-tools jfsutils cryptsetup lvm2 udftools