convert GPLv3+ license to SPDX

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

dc3dd.spec

@@ -1,9 +1,10 @@
 Name:           dc3dd
 Version:        7.3.1
-Release:        5%{?dist}
+Release:        6%{?dist}
 Summary:        Patched version of GNU dd for use in computer forensics
 
-License:        GPLv3+
+# Automatically converted from old format: GPLv3+ - review is highly recommended.
+License:        GPL-3.0-or-later
 URL:            http://sourceforge.net/projects/dc3dd/
 Source0:        http://downloads.sourceforge.net/dc3dd/%{name}-%{version}.zip
 
@@ -79,6 +80,9 @@ make install DESTDIR=$RPM_BUILD_ROOT
 %{_mandir}/man1/%{name}.*
 
 %changelog
+* Thu Jul 25 2024 Miroslav Suchý <msuchy@redhat.com> - 7.3.1-6
+- convert license to SPDX
+
 * Wed Jul 17 2024 Fedora Release Engineering <releng@fedoraproject.org> - 7.3.1-5
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_41_Mass_Rebuild