fix(postgresql): correct tmpfiles user from 'postgresql' to 'postgres'

services/postgresql.nix

@@ -11,7 +11,7 @@
       config.services.postgresql.dataDir
     ])
     (lib.serviceFilePerms "postgresql" [
-      "Z ${config.services.postgresql.dataDir} 0700 postgresql postgresql"
+      "Z ${config.services.postgresql.dataDir} 0700 postgres postgres"
     ])
   ];