6 files declare their use of Graph

ConfigDependencyManager.php in core/lib/Drupal/Core/Config/Entity/ConfigDependencyManager.php
Finder.php in core/lib/Drupal/Core/DefaultContent/Finder.php
MigrationPluginManager.php in core/modules/migrate/src/Plugin/MigrationPluginManager.php
ModuleHandler.php in core/lib/Drupal/Core/Extension/ModuleHandler.php
update.inc in core/includes/update.inc
Drupal database update API.
WorkspaceRepository.php in core/modules/workspaces/src/WorkspaceRepository.php