Add license information to files in matrix-base

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

roles/custom/matrix-base/tasks/validate_config.yml

@@ -1,3 +1,13 @@
+# SPDX-FileCopyrightText: 2018 - 2024 Slavi Pantaleev
+# SPDX-FileCopyrightText: 2020 - 2021 Aaron Raimist
+# SPDX-FileCopyrightText: 2020 Christian Wolf
+# SPDX-FileCopyrightText: 2020 Horvath Gergely
+# SPDX-FileCopyrightText: 2022 Charles Wright
+# SPDX-FileCopyrightText: 2022 Warren Bailey
+# SPDX-FileCopyrightText: 2023 Jayesh Nirve
+#
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
 ---
 
 - name: Fail if invalid homeserver implementation