13 files declare their use of UriInterface in Zircon Profile 8

Client.php in vendor/guzzlehttp/guzzle/src/Client.php

ClientInterface.php in vendor/guzzlehttp/guzzle/src/ClientInterface.php

DefaultFetcher.php in core/modules/aggregator/src/Plugin/aggregator/fetcher/DefaultFetcher.php

Contains \Drupal\aggregator\Plugin\aggregator\fetcher\DefaultFetcher.

functions.php in vendor/guzzlehttp/psr7/src/functions.php

locale.batch.inc in core/modules/locale/locale.batch.inc

Batch process to check the availability of remote or local po files.

RedirectMiddleware.php in vendor/guzzlehttp/guzzle/src/RedirectMiddleware.php

RedirectResponse.php in vendor/zendframework/zend-diactoros/src/Response/RedirectResponse.php

Request.php in vendor/guzzlehttp/psr7/src/Request.php

RequestTrait.php in vendor/zendframework/zend-diactoros/src/RequestTrait.php

ServerRequest.php in vendor/symfony/psr-http-message-bridge/Tests/Fixtures/ServerRequest.php

TransferStats.php in vendor/guzzlehttp/guzzle/src/TransferStats.php

Uri.php in vendor/zendframework/zend-diactoros/src/Uri.php

Uri.php in vendor/guzzlehttp/psr7/src/Uri.php