Make uncopyrightable files CC0

.gitignore

 # SPDX-FileCopyrightText: 2012-2017 Bruce Cowan <bruce@bcowan.me.uk>
 #
-# SPDX-License-Identifier: GPL-3.0-or-later
+# SPDX-License-Identifier: CC0-1.0
 
 .flatpak*
 

data/uk.me.bcowan.Rugby.desktop

 # SPDX-FileCopyrightText: 2020-2021 Bruce Cowan <bruce@bcowan.me.uk>
 #
-# SPDX-License-Identifier: GPL-3.0-or-later
+# SPDX-License-Identifier: CC0-1.0
 
 [Desktop Entry]
 Name=Rugby

data/uk.me.bcowan.Rugby.gresource.xml

@@ -2,7 +2,7 @@
 <!--
   SPDX-FileCopyrightText: 2012-2023 Bruce Cowan <bruce@bcowan.me.uk>
 
-  SPDX-License-Identifier: GPL-3.0-or-later
+  SPDX-License-Identifier: CC0-1.0
 -->
 <gresources>
   <gresource prefix="/uk/me/bcowan/Rugby">

data/uk.me.bcowan.Rugby.metainfo.xml

@@ -3,7 +3,7 @@
 <!--
 SPDX-FileCopyrightText: 2023-2024 Bruce Cowan
 
-SPDX-License-Identifier: GPL-3.0-or-later
+SPDX-License-Identifier: CC0-1.0
 -->
 
 <component type="desktop-application">
@@ -13,7 +13,7 @@ SPDX-License-Identifier: GPL-3.0-or-later
   <developer_name>Bruce Cowan</developer_name>
   <summary>Find possibilities for rugby scores</summary>
 
-  <metadata_license>CC-BY-SA-4.0</metadata_license>
+  <metadata_license>CC0-1.0</metadata_license>
   <project_license>GPL-3.0-or-later</project_license>
 
   <description>