Update docs/playbook-tags.md: add a copyright header

The original author can be seen here: 66a812d99c12cb24f38f57fb271875ca80a9d4cc/docs/installing.md#L12-L35

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

docs/playbook-tags.md

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+SPDX-FileCopyrightText: 2018 - 2022 Slavi Pantaleev
+SPDX-FileCopyrightText: 2024 - 2025 Suguru Hirahara
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+SPDX-License-Identifier: AGPL-3.0-or-later
+-->
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 # Playbook tags
 
 The Ansible playbook's tasks are tagged, so that certain parts of the Ansible playbook can be run without running all other tasks.