fix gomod

Author: techknowlogick

go.mod

@@ -2,6 +2,8 @@ module code.gitea.io/gitea
 
 go 1.23.0
 
+toolchain go1.23.6
+
 // rfc5280 said: "The serial number is an integer assigned by the CA to each certificate."
 // But some CAs use negative serial number, just relax the check. related:
 // Default TLS cert uses negative serial number #895 https://github.com/microsoft/mssql-docker/issues/895