FIPS POST: Change PBKDF2 CAST to use less iterations.

FIPS POST: Change PBKDF2 CAST to use less iterations.

Fixes #26876

The issue here is that the pbkdf2 'lower_bounds_checks' currently errors by default
in FIPS mode if iterations < 1000.
i.e. the "pkcs5" flag = 0 triggers an error..
Turning the flag on means the FIPS indicator is triggered (which is probably correct behaviour)
Not sure testing the fips state here is a good idea (i.e. taking a TSAN hit).

Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26887)