feat: reuse compliance for python files (#5440)

Adds reuse compliance checks for python files only, using `reuse lint-file`.

It is managed as a pre-commit hook, and hence ran in ci.

Over time we may add more files to be covered, but I suspect we would use something like `reuse.toml` for setting the licensing for `xml/xhtml/xsl` files, as there are just too many for adding the same text snippet to each to be justifiable.

Co-authored-by: Darragh Elliott <me@delliott.net>
Reviewed-on: #5440
Co-authored-by: delliott <delliott@fsfe.org>
Co-committed-by: delliott <delliott@fsfe.org>

build/fsfe_website_build_tests/lib/misc_test.py

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: Free Software Foundation Europe e.V. <https://fsfe.org>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
 import subprocess
 from pathlib import Path
 from time import sleep

build/fsfe_website_build_tests/lib/process_file_test.py

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: Free Software Foundation Europe e.V. <https://fsfe.org>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
 import textwrap
 from pathlib import Path