CI: Fix Steam upload again

After bf48a84d1ccdd564e2ea2b9cfc6722dc08b38092, the scheduled nightly
runs began to fail because the filenames of the artifacts had changed.
This would also have caused uploads on tag to fail. Explicitly specify
the asset architecture here. Windows arm64 builds are still ignored for
Steam Upload for now.

.github/actions/steam-upload/action.yaml

@@ -168,7 +168,7 @@ runs:
 
         print '::group::Prepare Windows x64 assets'
         mkdir -p steam-windows && pushd steam-windows
-        unzip ${root_dir}/(#i)obs-studio-*-windows.zip
+        unzip ${root_dir}/(#i)obs-studio-*-windows-x64.zip
         rm ${root_dir}/(#i)obs-studio-*-windows*.zip
 
         cp -r ${root_dir}/build-aux/steam/scripts_windows scripts