Issue #3184545 by Matroskeen: Return value is expected to be...

Issue #3184545 by Matroskeen: Return value is expected to be 'MigratePluginManager', 'MigrationPluginManagerInterface' returned

(cherry picked from commit 1d0d743f)

core/modules/migrate/src/Plugin/Migration.php

@@ -459,8 +459,8 @@ public function checkRequirements() {
   /**
    * Gets the migration plugin manager.
    *
-   * @return \Drupal\migrate\Plugin\MigratePluginManager
-   *   The plugin manager.
+   * @return \Drupal\migrate\Plugin\MigrationPluginManagerInterface
+   *   The migration plugin manager.
    */
   protected function getMigrationPluginManager() {
     return $this->migrationPluginManager;