Issue #3030902 by Krzysztof Domański, amateescu, xjm: Random fail in EntityReferenceAdminTest

(cherry picked from commit 8d89da6bc788684a5ffd032334a0ceea06ec85b8)

core/modules/field_ui/tests/src/Traits/FieldUiTestTrait.php

@@ -27,7 +27,10 @@ trait FieldUiTestTrait {
    *   settings' form).
    */
   public function fieldUIAddNewField($bundle_path, $field_name, $label = NULL, $field_type = 'test_field', array $storage_edit = [], array $field_edit = []) {
-    $label = $label ?: $this->randomString();
+    // Generate a label containing only letters and numbers to prevent random
+    // test failure.
+    // See https://www.drupal.org/project/drupal/issues/3030902
+    $label = $label ?: $this->randomMachineName();
     $initial_edit = [
       'new_storage_type' => $field_type,
       'label' => $label,