Follow-up for #3361534: config validation errors in contrib modules should cause deprecation notices, not test failures

Problem/Motivation

Due to #3361534: KernelTestBase::$strictConfigSchema = TRUE and BrowserTestBase::$strictConfigSchema = TRUE do not actually strictly validate in core, some very eager contrib modules may already start seeing test failures like this (reported by @jibran over at #3361534-90: KernelTestBase::$strictConfigSchema = TRUE and BrowserTestBase::$strictConfigSchema = TRUE do not actually strictly validate!):

1) Drupal\Tests\dynamic_entity_reference\Kernel\DynamicEntityReferenceTestViewsTest::testDefaultConfig
There should be no errors in configuration 'views.view.test_dynamic_entity_reference_entity_test_mul_view'. Errors:
Schema key 0 failed with: [dependencies.module.0] Module 'entity_test' is not installed.

Failed asserting that Array &0 (
    0 => '[dependencies.module.0] Module 'entity_test' is not installed.'
) is true.

⚠️ That should not happen, because that would imply the introduction of config validation in Drupal 10.2 introduces significant disruption.

Steps to reproduce

1. cd DRUPAL_PROJECT_ROOT
   cd modules
   git clone https://git.drupalcode.org/project/dynamic_entity_reference.git
   cd dynamic_entity_reference
   git checkout 3.x
   # This is the last commit at the time this issue was opened.
   git reset --hard 15c0f2ebfc69de604927966a1eb291e1fe073a1d
   # Copy the diff at #3361534-90: KernelTestBase::$strictConfigSchema = TRUE and BrowserTestBase::$strictConfigSchema = TRUE do not actually strictly validate, including the trailing blank line.
   pbpaste | git apply -3v
   

2. Run Drupal\Tests\dynamic_entity_reference\Kernel\DynamicEntityReferenceTestViewsTest
3. You'll see:
   

   1) Drupal\Tests\dynamic_entity_reference\Kernel\DynamicEntityReferenceTestViewsTest::testDefaultConfig
   There should be no errors in configuration 'views.view.test_dynamic_entity_reference_entity_test_mul_view'. Errors:
   Schema key 0 failed with: [dependencies.module.0] Module 'entity_test' is not installed.
   
   Failed asserting that Array &0 (
       0 => '[dependencies.module.0] Module 'entity_test' is not installed.'
   ) is true.
   

Proposed resolution

1. Convert any validation errors in the case of running a contrib test to deprecation notices instead.
2. Update the existing CR at https://www.drupal.org/node/3364109 to show

Expected result after doing this for the steps to reproduce above:

Testing /Users/wim.leers/core/modules/contrib/dynamic_entity_reference/tests/src/Kernel
.                                                                   1 / 1 (100%)

Time: 00:01.713, Memory: 10.00 MB

OK (1 test, 5 assertions)

Remaining self deprecation notices (5)

  1x: The 'views.view.test_dynamic_entity_reference_entity_test_mul_view' configuration contains validation errors. Invalid config is deprecated in drupal:10.2.0 and will be required to be valid in drupal:11.0.0. The following validation errors were found:
		- [dependencies.module.0] Module 'entity_test' is not installed.
    1x in DynamicEntityReferenceTestViewsTest::testDefaultConfig from Drupal\Tests\dynamic_entity_reference\Kernel

  1x: The 'views.view.test_dynamic_entity_reference_entity_test_view' configuration contains validation errors. Invalid config is deprecated in drupal:10.2.0 and will be required to be valid in drupal:11.0.0. The following validation errors were found:
		- [dependencies.module.0] Module 'entity_test' is not installed.
    1x in DynamicEntityReferenceTestViewsTest::testDefaultConfig from Drupal\Tests\dynamic_entity_reference\Kernel

  1x: The 'views.view.test_dynamic_entity_reference_mul_entity_test_mul_view' configuration contains validation errors. Invalid config is deprecated in drupal:10.2.0 and will be required to be valid in drupal:11.0.0. The following validation errors were found:
		- [dependencies.module.0] Module 'entity_test' is not installed.
    1x in DynamicEntityReferenceTestViewsTest::testDefaultConfig from Drupal\Tests\dynamic_entity_reference\Kernel

  1x: The 'views.view.test_dynamic_entity_reference_mul_entity_test_view' configuration contains validation errors. Invalid config is deprecated in drupal:10.2.0 and will be required to be valid in drupal:11.0.0. The following validation errors were found:
		- [dependencies.module.0] Module 'entity_test' is not installed.
    1x in DynamicEntityReferenceTestViewsTest::testDefaultConfig from Drupal\Tests\dynamic_entity_reference\Kernel

  1x: The 'views.view.test_dynamic_entity_reference_entity_test_rev_view' configuration contains validation errors. Invalid config is deprecated in drupal:10.2.0 and will be required to be valid in drupal:11.0.0. The following validation errors were found:
		- [dependencies.module.0] Module 'entity_test' is not installed.
    1x in DynamicEntityReferenceTestViewsTest::testDefaultConfig from Drupal\Tests\dynamic_entity_reference\Kernel

Process finished with exit code 1

Remaining tasks

1. ✅ Working MR
2. ✅ Reviews → #9 + #10
3. Once approved or committed by a core committer:
   1. ✅ tweak the release notes snippet in #3361534
   2. ✅ move the 10.2.0 release highlights tag to #3361534, and remove it here
   3. ✅ update the CR for #3361534 (i.e. https://www.drupal.org/node/3362879) to explain contrib modules' tests will start seeing deprecation notices rather than test failures, and add this issue as a related issue

User interface changes

None.

API changes

None.

Data model changes

None.

Release notes snippet

See #3361534: KernelTestBase::$strictConfigSchema = TRUE and BrowserTestBase::$strictConfigSchema = TRUE do not actually strictly validate.