Switch to SPDX license identifier

https://docs.fedoraproject.org/en-US/packaging-guidelines/LicensingGuidelines/#_license_field

libplacebo.spec

@@ -5,7 +5,7 @@ Version:        6.338.2
 Release:        %autorelease
 Summary:        Reusable library for GPU-accelerated video/image rendering primitives
 
-License:        LGPLv2+
+License:        LGPL-2.0-or-later
 URL:            https://github.com/haasn/libplacebo
 Source0:        %{url}/archive/v%{version}%{?prerelease}/%{name}-%{version}%{?prerelease}.tar.gz