Add license header.

Author: mportiz08

tests/unit/mixins/referencesProvider.spec.js

@@ -1,3 +1,12 @@
+/**
+ * This source file is part of the Swift.org open source project
+ *
+ * Copyright (c) 2024 Apple Inc. and the Swift project authors
+ * Licensed under Apache License v2.0 with Runtime Library Exception
+ *
+ * See https://swift.org/LICENSE.txt for license information
+ * See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
 import { shallowMount } from '@vue/test-utils';
 import referencesProvider from 'docc-render/mixins/referencesProvider';