build: upload xz-compressed artifacts.

tar doesn't compress on its own, it's just a container format. It
doesn't look like these 2 files are actually used otherwise, apart from
being log artifacts (at least I couldn't find any script decompressing
these).

This is an attempt to reduce size of artifacts on deps-flatpak because
CI complains with a "Request Entity Too Large" error.

.gitlab-ci.yml

@@ -413,8 +413,8 @@ deps-flatpak:
     paths:
       - _build-$RUNNER.tar.zst
       - flatpak-builder.log
-      - babl-meson-log.tar
-      - gegl-meson-log.tar
+      - babl-meson-log.tar.xz
+      - gegl-meson-log.tar.xz
     expire_in: 2 hours
 
 gimp-flatpak:

build/linux/flatpak/1_build-deps-flatpakbuilder.sh

@@ -79,7 +79,7 @@ printf "\e[0Ksection_start:`date +%s`:babl_build[collapsed=true]\r\e[0KBuilding
 eval $FLATPAK_BUILDER --force-clean --disable-rofiles-fuse --keep-build-dirs --build-only --stop-at=gegl \
                       "$GIMP_PREFIX" build/linux/flatpak/org.gimp.GIMP-nightly.json
 if [ "$GITLAB_CI" ]; then
-  tar cf babl-meson-log.tar .flatpak-builder/build/babl-1/_flatpak_build/meson-logs/meson-log.txt
+  tar cJf babl-meson-log.tar.xz .flatpak-builder/build/babl-1/_flatpak_build/meson-logs/meson-log.txt
 fi
 printf "\e[0Ksection_end:`date +%s`:babl_build\r\e[0K\n"
 
@@ -87,7 +87,7 @@ printf "\e[0Ksection_start:`date +%s`:gegl_build[collapsed=true]\r\e[0KBuilding
 eval $FLATPAK_BUILDER --force-clean --disable-rofiles-fuse --keep-build-dirs --build-only --stop-at=gimp \
                       "$GIMP_PREFIX" build/linux/flatpak/org.gimp.GIMP-nightly.json
 if [ "$GITLAB_CI" ]; then
-  tar cf gegl-meson-log.tar .flatpak-builder/build/gegl-1/_flatpak_build/meson-logs/meson-log.txt
+  tar cJf gegl-meson-log.tar.xz .flatpak-builder/build/gegl-1/_flatpak_build/meson-logs/meson-log.txt
   printf "\e[0Ksection_end:`date +%s`:gegl_build\r\e[0K\n"
 
   ## Save built deps for 'gimp-flatpak' job