8 files declare their use of StringInterface in Drupal 10

ConfigSchemaTest.php in core/tests/Drupal/KernelTests/Core/Config/ConfigSchemaTest.php

Email.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/Email.php

EntityFieldTest.php in core/tests/Drupal/KernelTests/Core/Entity/EntityFieldTest.php

PrimitiveTypeConstraintValidator.php in core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php

SchemaCheckTrait.php in core/lib/Drupal/Core/Config/Schema/SchemaCheckTrait.php

StringData.php in core/lib/Drupal/Core/TypedData/Plugin/DataType/StringData.php

TypedConfigTest.php in core/tests/Drupal/KernelTests/Config/TypedConfigTest.php

TypedDataTest.php in core/tests/Drupal/KernelTests/Core/TypedData/TypedDataTest.php