perl: run initLibStore() on openStore()

Since #7478 it's mandatory that `initLibStore()` is called for store
operations. However that's not the case when running `openStore()` in
Perl using the perl-bindings. That breaks e.g. `hydra-eval-jobset` when
built against Nix 2.13 which uses small portions of the store API.

perl/lib/Nix/Store.xs

@@ -26,6 +26,7 @@ static ref<Store> store()
  static std::shared_ptr<Store> _store;
  if (!_store) {
  try {
+ initLibStore();
  loadConfFile();
  settings.lockCPU = false;
  _store = openStore();