Graphql server composable schema can't be installed in kernel tests

I've just created a MR that updates the schema. Please review, thanks!

Thanks, can you add a simple kernel test so that we also have test coverage here?

I needed this patch in order to write the test for 🐛 Cache collision when multiple servers are using the same schema plugin Active because it was affected by the missing schema errors. So we could consider that the test in that issue also covers this one.

Agree with #5. Closing this issue in favor of https://www.drupal.org/project/graphql/issues/3491736 🐛 Cache collision when multiple servers are using the same schema plugin Active , which already applies fixes detected at this issue.