gitlab-ci: Add xz-utils for distribution tarballs

.gitlab-ci/Dockerfile

@@ -11,7 +11,8 @@ RUN apt-get update && \
         make gcc clang llvm libclang-rt-dev \
         zlib1g-dev liblzma-dev libgcrypt-dev \
         python3-dev \
-        cmake meson
+        cmake meson \
+        xz-utils
 WORKDIR /tests
 RUN curl https://www.w3.org/XML/Test/xmlts20080827.tar.gz |tar xz
 

MAINTAINERS.md

@@ -106,9 +106,9 @@ The following changes are allowed (after careful consideration):
 ## Updating the CI Docker image
 
 Note that the CI image is used for libxslt as well. First create a
-GitLab access token with `read_registry` and `write_registry`
-permissions. Then run the following commands with the Dockerfile in the
-.gitlab-ci directory:
+GitLab access token with maintainer rile and `read_registry` and
+`write_registry` permissions. Then run the following commands with the
+Dockerfile in the .gitlab-ci directory:
 
     docker login -u <username> -p <access_token> \
         registry.gitlab.gnome.org