gitlab-ci: install glib2-doc via "contrib/fedora/REQUIRED_PACKAGES"

We also generate a source tarball and artifact it.

Hence, we need proper gtk-doc links. This requires files in
/usr/share/gtk-doc/html for adding cross links. Install glib2-doc
package.

Note that in containers dnf is configured to not install documentation
files. We need to override that.

(cherry picked from commit a0f31e4038)

.gitlab-ci.yml

@@ -12,6 +12,11 @@ stages:
   before_script:
     - date '+%Y%m%d-%H%M%S'; NM_INSTALL="dnf install -y" ./contrib/fedora/REQUIRED_PACKAGES
     - date '+%Y%m%d-%H%M%S'; dnf install -y glibc-langpack-pl ccache clang
+
+    # containers have "tsflags=nodocs" in /etc/dnf/dnf.conf. We need /usr/shared/gtk-doc/html
+    # to generate proper documentation.
+    - date '+%Y%m%d-%H%M%S'; dnf reinstall -y --setopt='tsflags=' glib2-doc
+
     - date '+%Y%m%d-%H%M%S'; contrib/scripts/nm-ci-patch-gtkdoc.sh || true
 
 .debian_install: &debian_install

contrib/fedora/REQUIRED_PACKAGES

@@ -35,6 +35,7 @@ install \
     gcc-c++ \
     gettext-devel \
     git \
+    glib2-doc \
     gnutls-devel \
     gobject-introspection-devel \
     gtk-doc \