Update roles/custom/matrix-client-element/templates/env.j2: add the copyright header

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

roles/custom/matrix-client-element/templates/env.j2

@@ -1,3 +1,9 @@
+{#
+SPDX-FileCopyrightText: 2025 Slavi Pantaleev
+
+SPDX-License-Identifier: AGPL-3.0-or-later
+#}
+
 ELEMENT_WEB_PORT={{ matrix_client_element_environment_variable_element_web_port }}
 
 {{ matrix_client_element_environment_variables_extension }}