[9.20] fix: usr: Fix parsing bug in remote-servers with key or tls

The :any:`remote-servers` clause enable the following pattern using a named ``server-list``:

	remote-servers a { 1.2.3.4; ... };
	remote-servers b { a key foo; };

However, such configuration was wrongly rejected, with an "unexpected token 'foo'" error. Such configuration is now accepted.

Closes #5646

Backport of MR !11252

Merge branch 'backport-5646-fix-named-remote-servers-key-tls-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!11300