scripts: dl_github_archive: fix zstd args passed to tar

scripts: dl_github_archive: fix zstd args passed to tar

The multi-word zstd option '-I zstd -T0 --ultra -20' was appended as a
single argv element. subprocess passes each list element as one argv
entry, so tar received the whole string as one argument and failed to
recognize it. Split into separate '-I' and 'zstd -T0 --ultra -20'
elements so tar correctly interprets the compressor command.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24375
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>