Page title block should not be hidden on administrative pages

Patch ready for review!

Since this module only modifies nodes, the patch in #2 sufficiently matches the coverage. I was envisioning something more like the below, but this should work fine. Setting to "RTBC"!

  if (\Drupal::service('router.admin_context')->isAdminRoute()) {
    return;
  }

Automatically closed - issue fixed for 2 weeks with no activity.