7 files declare their use of Upsert

Connection.php in core/tests/fixtures/database_drivers/custom/fake/Connection.php
Connection.php in core/lib/Drupal/Core/Database/Connection.php
StubUpsert.php in core/tests/Drupal/Tests/Core/Database/Stub/StubUpsert.php
Upsert.php in core/modules/sqlite/src/Driver/Database/sqlite/Upsert.php
Upsert.php in core/modules/mysql/src/Driver/Database/mysql/Upsert.php
Upsert.php in core/modules/pgsql/src/Driver/Database/pgsql/Upsert.php
Upsert.php in core/tests/fixtures/database_drivers/module/core_fake/src/Driver/Database/CoreFakeWithAllCustomClasses/Upsert.php

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