convert license to SPDX

This is part of https://fedoraproject.org/wiki/Changes/SPDX_Licenses_Phase_4

parallel.spec

@@ -2,7 +2,8 @@ Name:           parallel
 Summary:        Shell tool for executing jobs in parallel
 Version:        20240722
 Release:        %autorelease
-License:        GFDL and GPLv3+
+# Automatically converted from old format: GFDL and GPLv3+ - review is highly recommended.
+License:        LicenseRef-Callaway-GFDL AND GPL-3.0-or-later
 URL:            https://www.gnu.org/software/parallel/
 Source0:        https://ftp.gnu.org/gnu/%{name}/%{name}-%{version}.tar.bz2
 BuildArch:      noarch