Add pkgconf and systemd before building/ installing

.gitlab-ci.yml:
Add pkgconf and systemd to the list of packages, that are installed
before executing the build and install targets. They are required to
retrieve the correct path for systemd's system units.

.gitlab-ci.yml

@@ -46,7 +46,7 @@ build_install:
   stage: test
   needs: []
   before_script:
-    - pacman -Syu --needed --noconfirm make python sequoia-sq
+    - pacman -Syu --needed --noconfirm make pkgconf python sequoia-sq systemd
   script:
     - make
     - make install PREFIX=/usr