fix: update security.txt expiry date (@norwd)

Author: norwd

frontend/static/.well-known/security.txt

@@ -1,6 +1,6 @@
 Contact: mailto:contact@monkeytype.com
 Contact: message @Miodec on discord.gg/monkeytype
-Expires: 2024-06-03T21:00:00.000Z
+Expires: 2026-12-31T23:59:59.999Z
 Preferred-Languages: en
 Canonical: https://monkeytype.com/.well-known/security.txt
 Policy: https://monkeytype.com/security-policy