package/ltp-testsuite: bump version to 20210524

Add locally computed sha256 (+ keep sha1 from github checksum file).

sysinfo.h fix patch is still needed (until Buildroot MUSL toolchain gets
updated).

Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>