unbound: disable trust anchor signaling

TA signaling in newer versions of Unbound breaks old tests
which do not contain answers for RFC 8145 queries.

This does not work with older versions of Unbound but hopefully these
are too old now for anyone to care.

template/unbound.j2

@@ -11,6 +11,7 @@
 # The server clause sets the main parameters.
 server:
 	# whitespace is not necessary, but looks cleaner.
+	trust-anchor-signaling: no
 
 	# verbosity number, 0 is least verbose. 1 is default.
 	verbosity: 3