Dedupe the WorkingDirectory path of the linux-builder

modules/nix/linux-builder.nix

@@ -11,6 +11,8 @@ let
     modules = [ cfg.config ];
   };
 
+  WorkingDirectory = "/var/lib/darwin-builder";
+
   # create-builder uses TMPDIR to share files with the builder, notably certs.
   # macOS will clean up files in /tmp automatically that haven't been accessed in 3+ days.
   # If we let it use /tmp, leaving the computer asleep for 3 days makes the certs vanish.
@@ -89,7 +91,7 @@ in
     } ];
 
     system.activationScripts.preActivation.text = ''
-      mkdir -p /var/lib/darwin-builder
+      mkdir -p ${WorkingDirectory}
     '';
 
     launchd.daemons.linux-builder = {
@@ -103,7 +105,7 @@ in
         ];
         KeepAlive = true;
         RunAtLoad = true;
-        WorkingDirectory = "/var/lib/darwin-builder";
+        inherit WorkingDirectory;
       };
     };