daemon/lua/trust_anchors: don't crash when dealing with unknown algorhitm

Closes #449 (closed)

• Depends on deckard!159 (merged)
• Depends on respdiff!52 (merged)

ci/respdiff/kresd.config

@@ -5,7 +5,7 @@ net.listen('127.0.0.1', 8853, { tls = true })
 net.ipv6=false
 
 -- Auto-maintain root TA
-trust_anchors.file = '.local/etc/knot-resolver/root.keys'
+trust_anchors.add_file('.local/etc/knot-resolver/root.keys')
 
 -- Large cache size, so we don't need to flush often
 -- This can be larger than available RAM, least frequently accessed