.github: register gettext as a dependency

Author: khorben

.github/workflows/deforaos-c-ci_ubuntu-latest.yml

@@ -17,6 +17,7 @@ jobs:
         sudo apt-get update
         sudo apt-get install -y \
           docbook-xsl \
+          gettext \
           gtk-doc-tools \
           libgtk-3-dev \
           libxml2-utils \