build_library/build_image_util.sh: Fix copy-pasta

We were supposed to collect allowed users and allowed groups into
separate arrays. Due to the copy-paste mistake, we overwrote allowed
users array with allowed groups while leaving the array for allowed
groups empty, so we ended up passing only allowed groups instead of
both.

Author: krnowak

build_library/build_image_util.sh

@@ -654,7 +654,7 @@ finish_image() {
   # --allow-user=root
   # --allow-user=core
   mapfile -t allowed_users < <(grep '^COPY_USERS=' "${root_fs_dir}/sbin/flatcar-tmpfiles" | sed -e 's/.*="\([^"]*\)"/\1/' | tr '|' '\n' | sed -e 's/^/--allow-user=/')
-  mapfile -t allowed_users < <(grep '^COPY_GROUPS=' "${root_fs_dir}/sbin/flatcar-tmpfiles" | sed -e 's/.*="\([^"]*\)"/\1/' | tr '|' '\n' | sed -e 's/^/--allow-group=/')
+  mapfile -t allowed_groups < <(grep '^COPY_GROUPS=' "${root_fs_dir}/sbin/flatcar-tmpfiles" | sed -e 's/.*="\([^"]*\)"/\1/' | tr '|' '\n' | sed -e 's/^/--allow-group=/')
   sudo "${BUILD_LIBRARY_DIR}/gen_tmpfiles.py" --root="${root_fs_dir}" \
       --output="${root_fs_dir}/usr/lib/tmpfiles.d/base_image_var.conf" \
       "${ignores[@]}" "${allowed_users[@]}" "${allowed_groups[@]}" "${root_fs_dir}/var"