Issue #3085604 by bircher, catch, alexpott: Protect against concurrent config transformations

core/modules/config_environment/config_environment.module

...odules/config_environment/config_environment.services.yml

...dules/config_environment/src/Core/Config/ConfigEvents.php

...nfig_environment/src/Core/Config/ExportStorageManager.php

..._environment/src/Core/Config/ImportStorageTransformer.php

...g_environment/src/Core/Config/StorageManagerInterface.php

...vironment/src/Core/Config/StorageTransformerException.php

...tests/src/Kernel/Core/Config/ExportStorageManagerTest.php

...s/src/Kernel/Core/Config/ImportStorageTransformerTest.php