Fix double escape

nix/mixins/aws.nix

@@ -8,7 +8,7 @@
         log_group_name = "ec2-logs";
         auto_create_group = true;
         log_stream_name = "default";
-        log_stream_template = "$${ec2_instance_id}";
+        log_stream_template = "\${ec2_instance_id}";
       }];
     };
   };