gitlab-ci: distribute the meson-generated tarball as well.

Maybe let's try to distribute the meson tarball next to the autotools
tarball for our next dev release, and announce that packagers are
invited to test the meson build from tarball and report back.

.gitlab-ci.yml

@@ -775,6 +775,34 @@ sources:
       sha512sum gimp-*.tar.bz2 > ${FILENAME}.SHA512SUMS
   needs: ["gimp-distcheck-debian"]
 
+sources-meson:
+  rules:
+    # On commits.
+    - if: '$CI_PIPELINE_SOURCE == "push"'
+    # On releases.
+    - if: '$CI_COMMIT_TAG != null'
+    # Custom builds though web GUI, API or schedules.
+    - if: '$GIMP_CI_SOURCES != null'
+  stage: distribution
+  dependencies:
+    - gimp-meson-debian
+  artifacts:
+    name: "GIMP-sources-meson-${CI_COMMIT_SHORT_SHA}"
+    when: always
+    expire_in: 2 days
+    paths:
+    - gimp-*.tar.xz
+    - gimp-*.tar.xz.SHA256SUMS
+    - gimp-*.tar.xz.SHA512SUMS
+  script:
+    - mv _build/meson-dist/gimp-*.tar.xz .
+    - BASENAME=`ls gimp-*.tar.xz | sed 's/.tar.xz//'`  &&
+      FILENAME="$BASENAME-meson.tar.xz"                &&
+      mv $BASENAME.tar.xz  $FILENAME                   &&
+      sha256sum gimp-*.tar.xz > ${FILENAME}.SHA256SUMS &&
+      sha512sum gimp-*.tar.xz > ${FILENAME}.SHA512SUMS
+  needs: ["gimp-meson-debian"]
+
 dev-docs:
   rules:
     # On commits.