fix: upgrade next from 12.1.0 to 12.3.4

Snyk has created this PR to upgrade next from 12.1.0 to 12.3.4.

See this package in npm:
https://www.npmjs.com/package/next

See this project in Snyk:
https://app.snyk.io/org/nft-772/project/2a91765d-a5d7-4b9d-81d1-8dad50cdf364?utm_source=github&utm_medium=referral&page=upgrade-pr

package.json

@@ -14,7 +14,7 @@
     "@govtechsg/open-attestation": "^6.3.0",
     "axios": "^0.24.0",
     "chrome-aws-lambda": "^5.5.0",
-    "next": "latest",
+    "next": "12.3.4",
     "puppeteer-core": "^13.4.0",
     "react": "^17.0.2",
     "react-dom": "^17.0.2",