ci: Use sudo to run pip install

We can't assume the script is run as root, so request the required
privileges where needed.

Fixes: 6bd76eec0c ("ci: Use common-dependencies script to install argcomplete")
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4234>

.gitlab-ci/install-common-dependencies.sh

@@ -42,7 +42,7 @@ pip_install() {
     local pypaths=($destdir/usr/lib*/python3*/site-packages)
     if ! pip3 list "${pypaths[@]/#/--path=}" | grep $pkg >/dev/null
     then
-      pip3 install --ignore-installed \
+      sudo pip3 install --ignore-installed \
         --root-user-action ignore \
         --prefix $destdir/usr \
         $pkg