tests/basic: use SHA256 instead of RMD160 for SHAKE extract testing

* tests/basic.c (check_one_md): Use GCRY_MD_SHA256 as 'crcalgo' for
SHAKE128/SHAKE256 testing.

RMD160 was used to calculate output checksum from two SHAKE extract
streams, which are run with different extract buffer size but for
same total length and with same input. Patch switches to use SHA256
for checksumming for FIPS support.

• GnuPG-bug-id: T5520
• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>