Use appropriate config schema

Problem/Motivation

The config schema is currently invalid, and is flagged on Drupal 11.

Steps to reproduce

Create a corresponding entity reference, and check it with the config inspector module, sample output:

$ drush config:inspect --detail --only-error --strict-validation --filter-keys=cer.corresponding_reference.directory
➜  🤖 Analyzing…

 Legend for Data:
  ✅❓  → Correct primitive type, detailed validation impossible.
  ✅✅  → Correct primitive type, passed all validation constraints.
 ------------------------------------------------------ ---------------- ------------- ------
  Key                                                    Status           Validatable   Data
 ------------------------------------------------------ ---------------- ------------- ------
  cer.corresponding_reference.directory:bundles.node.0   missing schema

Proposed resolution

Update the config schema.

Remaining tasks

Provide MR.