Add license to the version catalog toml file

Author: timofeys1

gradle/libs.versions.toml

@@ -1,3 +1,17 @@
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the Swift.org open source project
+##
+## Copyright (c) 2026 Apple Inc. and the Swift.org project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of Swift.org project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
 [versions]
 kotlinx-serialization = "1.7.3"
 junit-version = "5.10.0"