Add remaining copyright statements, add licenses sanity test (#5098)

* Add sanity test (currently fails).

* doc_fragments can also be non-GPLv3+.

* Replace 'Author:' by 'Copyright:' in some specific cases.

* Avoid matching string for license checkers.

* Reformulate not to throw license detection off.

* Add PSF copyright notice for plugins/module_utils/_mount.py.

* Add generic copyright notices.

* Update changelog fragment.

tests/unit/plugins/modules/system/test_gconftool2_info.py

@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
-# Author: Alexei Znamensky (russoz@gmail.com)
+# Copyright (c) Alexei Znamensky (russoz@gmail.com)
 # GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
 # SPDX-License-Identifier: GPL-3.0-or-later
 

tests/unit/plugins/modules/system/test_xfconf.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
-# Author: Alexei Znamensky (russoz@gmail.com)
-# Largely adapted from test_redhat_subscription by
-# Jiri Hnidek (jhnidek@redhat.com)
+# Copyright (c) Alexei Znamensky (russoz@gmail.com)
+# Largely adapted from test_redhat_subscription:
+# Copyright (c) Jiri Hnidek (jhnidek@redhat.com)
 #
 # GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
 # SPDX-License-Identifier: GPL-3.0-or-later

tests/unit/plugins/modules/system/test_xfconf_info.py

@@ -1,4 +1,4 @@
-# Author: Alexei Znamensky (russoz@gmail.com)
+# Copyright (c) Alexei Znamensky (russoz@gmail.com)
 # GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
 # SPDX-License-Identifier: GPL-3.0-or-later