pkg/debian: Enforce XZ compression for package

.github/workflows/debian.yml

@@ -92,6 +92,8 @@ jobs:
         cp keys/surface.crt debian/kernel/linux/keys/MOK.crt
 
     - name: Build kernel
+      env:
+        KDEB_COMPRESS: xz
       run: |
         cd pkg/debian/kernel/linux
         make bindeb-pkg -j2