Issue #3480275 by benjifisher, heddn: File validation changed in Drupal 10.2

migrate_source_ui.info.yml

 name: Migrate Source UI
 type: module
 description: UI for CSV, XML or JSON sources.
-core_version_requirement: ^10.1 || ^11
+core_version_requirement: ^10.2 || ^11
 package: Migrate
 configure: migrate_source_ui.form
 

src/Form/MigrateSourceUiForm.php

@@ -107,8 +107,8 @@ class MigrateSourceUiForm extends FormBase {
       '#type' => 'file',
       '#title' => $this->t('Upload the source file'),
       '#upload_validators' => [
-        'file_validate_extensions' => [
-          'json csv xml',
+        'FileExtension' => [
+          'extensions' => 'json csv xml',
         ],
       ],
     ];
@@ -135,7 +135,7 @@ class MigrateSourceUiForm extends FormBase {
     $migrationInstance = $this->pluginManagerMigration->createStubMigration($definition);
     $extension = $this->getFileExtensionSupported($migrationInstance);
 
-    $validators = ['file_validate_extensions' => [$extension]];
+    $validators = ['FileExtension' => ['extensions' => $extension]];
     // Check to see if a specific file temp directory is configured. If not,
     // default the value to FALSE, which will instruct file_save_upload() to
     // use Drupal's temporary files scheme.