Missing schema after 8.3.x upgrade

[nitesh-voya]

Describe the bug
This issue is referenced from d.o issues https://www.drupal.org/project/search_api_pantheon/issues/3505380

First issue is related to schema
Drupal\Core\Config\Schema\SchemaIncompleteException: Schema errors for search_api.server.pantheon_search with the following errors: search_api.server.pantheon_search:backend_config.connector_config missing schema, search_api.server.pantheon_search:backend_config.disabled_request_handlers variable type is NULL but applied schema class is Drupal\Core\Config\Schema\Sequence, search_api.server.pantheon_search:backend_config.disabled_request_dispatchers variable type is NULL but applied schema class is Drupal\Core\Config\Schema\Sequence

To Reproduce
Steps to reproduce the behavior:
Steps to reproduce the behavior:

• Write an automated (functional) test that installs search_api_pantheon
• Run the automated test and observe the failure.

Screenshot

Expected behavior
Automated testing should not flag an invalid schema.
Screenshots

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.