build, gitlab: name artifact folder per arch.

Apparently that is the reason why the Aarch64 jobs are rebuilding
everything, though I'm not sure to understand why (can gimp-flatpak job
grab the deps-flatpak artifacts from the wrong architecture?).

.gitlab-ci.yml

@@ -411,7 +411,7 @@ deps-flatpak:
     - sh build/linux/flatpak/1_build-deps-flatpakbuilder.sh
   artifacts:
     paths:
-      - flatpak-builder-deps
+      - flatpak-builder-$RUNNER
       - flatpak-builder.log*
       - babl-meson-log.xz
       - gegl-meson-log.xz

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

@@ -113,6 +113,6 @@ if [ "$GITLAB_CI" ]; then
     tar --zstd --xattrs -cf "$dir.tar.zst" "$dir"
     rm -fr "$dir"
   done
-  rm -fr flatpak-builder-deps
-  mv .flatpak-builder flatpak-builder-deps
+  rm -fr flatpak-builder-$RUNNER
+  mv .flatpak-builder flatpak-builder-$RUNNER
 fi

build/linux/flatpak/2_build-gimp-flatpakbuilder.sh

@@ -23,8 +23,8 @@ eval "$(sed -n '/Install part/,/End of check/p' build/linux/flatpak/1_build-deps
 
 if [ "$GITLAB_CI" ]; then
   # Extract deps from previous job
-  for archive in flatpak-builder-deps/*; do
-    if [ "$archive" != "flatpak-builder-deps/build" ]; then
+  for archive in flatpak-builder-$RUNNER/*; do
+    if [ "$archive" != "flatpak-builder-$RUNNER/build" ]; then
       tar --zstd -xf "$archive"
     fi
   done