ci: compress squashfs with zstd

Compress squashfs with zstd since that now we have
CONFIG_SQUASHFS_ZSTD=y in all our guest kernels.

In my tests it is 78MB vs 85MB (an 8.2% reduction)

Signed-off-by: Pablo Barbáchano <[email protected]>

Author: pb8o

resources/rebuild.sh

@@ -67,10 +67,9 @@ EOF
     id_rsa=$OUTPUT_DIR/$ROOTFS_NAME.id_rsa
     sudo cp id_rsa $id_rsa
 
-    # -comp zstd but guest kernel does not support
     rootfs_img="$OUTPUT_DIR/$ROOTFS_NAME.squashfs"
     sudo mv $rootfs/root/manifest $OUTPUT_DIR/$ROOTFS_NAME.manifest
-    sudo mksquashfs $rootfs $rootfs_img -all-root -noappend
+    sudo mksquashfs $rootfs $rootfs_img -all-root -noappend -comp zstd
     sudo rm -rf $rootfs
     sudo chown -Rc $USER. $OUTPUT_DIR
 }