ci: use xz compress

Signed-off-by: Han Gao <gaohan@iscas.ac.cn>

Author: RevySR

.github/workflows/kernel.yml

@@ -11,7 +11,7 @@ env:
   board: th1520
   KBUILD_BUILD_USER: builder
   KBUILD_BUILD_HOST: revyos-riscv-builder
-  KDEB_COMPRESS: none
+  KDEB_COMPRESS: xz
   KDEB_CHANGELOG_DIST: unstable
 
 jobs: