fix: usr: Reject RRSIG records covering meta-types

A recursive resolver could accept and cache an RRSIG record whose
Type-Covered field names a meta-type (ANY, AXFR, IXFR, MAILA, MAILB),
even though no real RRset of those types ever exists. Such records
are now rejected by the DNS message parser.

Closes #6002

Merge branch '6002-reject-rrsig-covering-meta-types' into 'main'

See merge request isc-projects/bind9!12048