Add missing eu-north-1 to lambda mapping

Author: Lachlan Donald

templates/aws-stack.yml

@@ -467,6 +467,7 @@ Mappings:
     eu-west-1 : { Bucket: "buildkite-lambdas-eu-west-1" }
     eu-west-2 : { Bucket: "buildkite-lambdas-eu-west-2" }
     eu-west-3 : { Bucket: "buildkite-lambdas-eu-west-3" }
+    eu-north-1 : { Bucket: "buildkite-lambdas-eu-north-1" }
     sa-east-1 : { Bucket: "buildkite-lambdas-sa-east-1" }
 
   # Generated from Makefile via build/mappings.yml