chore: add REUSE headers to catalog.yaml

Add SPDX license and copyright headers to comply with REUSE specification.

Signed-off-by: Vitor Mattos <[email protected]>

Author: vitormattos

tests/php/fixtures/pdfs/catalog.yaml

@@ -1,5 +1,8 @@
+# SPDX-FileCopyrightText: 2025 LibreCode coop and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
 # LibreSign PDF Test Fixtures Catalog
-# 
+#
 # This file describes all PDF test fixtures used in the test suite.
 # Each entry provides detailed metadata about the PDF signature characteristics.
 #