nixos/pam: Fix apparmor syntax error

When running e.g. `aa-genprof` get error:

> ERROR: Syntax Error: Unknown line found in file /etc/apparmor.d/abstractions/pam line 26:
>     r /nix/store/XXXXX.pam,mr /nix/store/XXXXX-linux-pam-1.5.1/lib/security/pam_filter/*,

So add an explicit newline as concatMapStringsSep only adds them
between.

nixos/modules/security/pam.nix

@@ -1072,8 +1072,8 @@ in
     security.apparmor.includes."abstractions/pam" = let
       isEnabled = test: fold or false (map test (attrValues config.security.pam.services));
       in
-      lib.concatMapStringsSep "\n"
-        (name: "r ${config.environment.etc."pam.d/${name}".source},")
+      lib.concatMapStrings
+        (name: "r ${config.environment.etc."pam.d/${name}".source},\n")
         (attrNames config.security.pam.services) +
       ''
       mr ${getLib pkgs.pam}/lib/security/pam_filter/*,