[libxml2] Move Dockerfile to .gitlab-ci directory

[Nick Wellnhofer <nwellnhof src gnome org>]

commit efc0e85c02071a88a2ef5d1d0caace166790d645
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sun Sep 4 15:26:47 2022 +0200

    Move Dockerfile to .gitlab-ci directory

 .gitlab-ci.yml        | 16 ----------------
 .gitlab-ci/Dockerfile | 16 ++++++++++++++++
 MAINTAINERS.md        | 21 +++------------------
 3 files changed, 19 insertions(+), 34 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index fea29bf5..5cde8b36 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,20 +1,4 @@
 .test:
-  # The image was generated with the following Dockerfile. It is also used
-  # for libxslt, that's why we need git and libgcrypt-dev.
-  #
-  # FROM ubuntu:20.04
-  # ENV DEBIAN_FRONTEND=noninteractive
-  # RUN apt-get update && \
-  #     apt-get upgrade -y && \
-  #     apt-get install -y --no-install-recommends \
-  #         curl git ca-certificates \
-  #         autoconf automake libtool pkg-config \
-  #         make gcc clang llvm \
-  #         zlib1g-dev liblzma-dev libgcrypt-dev \
-  #         python-dev python3-dev \
-  #         cmake
-  # WORKDIR /tests
-  # RUN curl https://www.w3.org/XML/Test/xmlts20080827.tar.gz |tar xz
   image: registry.gitlab.gnome.org/gnome/libxml2
   variables:
     BASE_CONFIG: "--with-ftp --with-legacy --with-xptr-locs"
diff --git a/.gitlab-ci/Dockerfile b/.gitlab-ci/Dockerfile
new file mode 100644
index 00000000..102657bd
--- /dev/null
+++ b/.gitlab-ci/Dockerfile
@@ -0,0 +1,16 @@
+# The image is also used for libxslt, that's why we need git and
+# libgcrypt-dev.
+
+FROM ubuntu:22.04
+ENV DEBIAN_FRONTEND=noninteractive
+RUN apt-get update && \
+    apt-get upgrade -y && \
+    apt-get install -y --no-install-recommends \
+        curl git ca-certificates \
+        autoconf automake libtool pkg-config \
+        make gcc clang llvm \
+        zlib1g-dev liblzma-dev libgcrypt-dev \
+        python2-dev python3-dev \
+        cmake
+WORKDIR /tests
+RUN curl https://www.w3.org/XML/Test/xmlts20080827.tar.gz |tar xz
diff --git a/MAINTAINERS.md b/MAINTAINERS.md
index 89d00fb3..2d9204e8 100644
--- a/MAINTAINERS.md
+++ b/MAINTAINERS.md
@@ -56,25 +56,10 @@ xml gnome org.
 ## Updating the CI Docker image
 
 Note that the CI image is used for libxslt as well. Run the following
-commands with the Dockerfile passed as heredoc:
+commands with the Dockerfile in the .gitlab-ci directory:
 
     docker login registry.gitlab.gnome.org
-
-    docker build -t registry.gitlab.gnome.org/gnome/libxml2 - <<'EOF'
-    FROM ubuntu:22.04
-    ENV DEBIAN_FRONTEND=noninteractive
-    RUN apt-get update && \
-       apt-get upgrade -y && \
-       apt-get install -y --no-install-recommends \
-           curl git ca-certificates \
-           autoconf automake libtool pkg-config \
-           make gcc clang llvm \
-           zlib1g-dev liblzma-dev libgcrypt-dev \
-           python2-dev python3-dev \
-           cmake
-    WORKDIR /tests
-    RUN curl https://www.w3.org/XML/Test/xmlts20080827.tar.gz |tar xz
-    EOF
-
+    docker build -t registry.gitlab.gnome.org/gnome/libxml2 - \
+        < .gitlab-ci/Dockerfile
     docker push registry.gitlab.gnome.org/gnome/libxml2