fix: dns-json response.Answer may be undefined

This fixes an error seen in CI when response.Answer.filter() was called
and we got an error:

  TypeError: Cannot read properties of undefined (reading 'filter')
    at findDNSLinkAnswer (file:///home/runner/work/helia-ipns/helia-ipns/packages/ipns/src/utils/dns.ts:45:34)
    at ipfsPath (file:///home/runner/work/helia-ipns/helia-ipns/packages/ipns/src/utils/dns.ts:29:18)
    at httpQueue.add.signal (file:///home/runner/work/helia-ipns/helia-ipns/packages/ipns/src/dns-resolvers/dns-json-over-https.ts:71:22)

packages/ipns/src/utils/dns.ts

@@ -22,7 +22,7 @@ export interface DNSResponse {
   AD: boolean
   CD: boolean
   Question: Question[]
-  Answer: Answer[]
+  Answer?: Answer[]
 }
 
 export const ipfsPath = (domain: string, response: DNSResponse): string => {
@@ -42,7 +42,7 @@ export const ipfsPath = (domain: string, response: DNSResponse): string => {
 }
 
 export const findDNSLinkAnswer = (domain: string, response: DNSResponse): Answer => {
-  const answer = response.Answer.filter(a => a.data.includes('dnslink=/ipfs') || a.data.includes('dnslink=/ipns')).pop()
+  const answer = response.Answer?.filter(a => a.data.includes('dnslink=/ipfs') || a.data.includes('dnslink=/ipns')).pop()
 
   if (answer == null) {
     throw new CodeError(`No dnslink records found for domain: ${domain}`, 'ERR_DNSLINK_NOT_FOUND')