chore(reuse): add spdx headers to psalm baseline

Signed-off-by: Vitor Mattos <vitor@php.rio>

Author: vitormattos

tests/psalm-baseline.xml

@@ -1,4 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
+<!-- SPDX-FileCopyrightText: 2026 LibreCode coop and contributors -->
+<!-- SPDX-License-Identifier: AGPL-3.0-or-later -->
 <files psalm-version="6.16.1@f1f5de594dc76faf8784e02d3dc4716c91c6f6ac">
   <file src="src/Http/NfseClient.php">
     <MissingOverrideAttribute>