After commit f4eb3ba4, that is part of removing 'auto-dnssec', the
inline system test started to fail in FIPS CI jobs. This is because
the 'nsec3-loop' zone started to use a RSASHA256 key size of 1024 and
this is not FIPS compliant.
This commit changes the key size from 1024 to 4096, in order to
become FIPS compliant again.