Ensure static stub NS records are not returned

static-stub synthesises NS record which shouldn't be returned to clients. Normally the NS records from the actual zone will be returned but not always.

• Setup a static-stub for "com" and disable minimal responses.
• query for foo.com NS (TTL is 600)
• wait 120 seconds
• query for foo.com A (TTL is 600)
• wait 500 seconds
• query for foo.com A

; <<>> DiG 9.19.20-dev <<>> foo.com -p 5555
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18858
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; COOKIE: dddb220761d487fa0100000065dec10ee6a221e99d9baa11 (good)
;; QUESTION SECTION:
;foo.com.			IN	A

;; ANSWER SECTION:
foo.com.		100	IN	A	34.206.39.153

;; AUTHORITY SECTION:
com.			86400	IN	NS	com.

;; Query time: 2 msec
;; SERVER: ::1#5555(::1) (UDP)
;; WHEN: Wed Feb 28 16:13:50 AEDT 2024
;; MSG SIZE  rcvd: 94