[9.20] fix: usr: Stop caching lack of EDNS support

`named` could falsely learn that a server doesn't support EDNS when
a spoofed response was received; that subsequently prevented DNSSEC
lookups from being made. This has been fixed.

Backport of MR !776

Closes https://gitlab.isc.org/isc-projects/bind9/-/issues/3949

Closes https://gitlab.isc.org/isc-projects/bind9/-/issues/5066

Merge branch 'backport-5066-stop-caching-lack-of-edns-support-9.20' into 'v9.20.8-release'

See merge request isc-private/bind9!782