s3:tests: Fix argument checks in test shell scripts

s3:tests: Fix argument checks in test shell scripts

Fix the argument count check to match the number of required
positional parameters.

Sample failure:
[595(5736)/3145 at 15m52s, 1 errors] samba3.blackbox.update_keytab(ad_member_idmap_nss:local)
source3/script/tests/test_update_keytab.sh: line 16: shift: 2: shift count out of range

Pair-Programmed-With: Anoop C S <anoopcs@samba.org>
Signed-off-by: Andreas Schneider <asn@samba.org>
Signed-off-by: Anoop C S <anoopcs@samba.org>
Autobuild-User(master): Anoop C S <anoopcs@samba.org>
Autobuild-Date(master): Sat Jun 13 10:30:59 UTC 2026 on atb-devel-224