Cover the module with node tests (The combination of values)

We should create new tests to check the combination of values in the config.
I guess steps should be smth like:
- create a regular user with permission to create nodes
- create a new content type with two text fields
- add configs - both text fields should be unique (combination)
- submit the node form with the text field 1 = test & text field 2 = test
- the node should be created without any errors
- submit the node form with the text field 1 = test & text field 2 = test
- the user should have an error message
- add a 'unique_field_perm_bypass' permission to the user
- submit the node form with the text field 1 = test & text field 2 = test
- the node should be created without any errors

code can be extended from #3569544: Cover the module with node tests