Update the License tag to use SPDX license expressions

Examine the zsh source and construct a new License tag using SPDX
identifiers.  Most of the zsh source is licensed under what SPDX calls
the MIT-Modern-Variant license.  One source file
(openssh_bsd_setres_id.c) carries an ISC license as well.  Three shell
extensions are licensed under GPL-2.0-only.

Signed-off-by: David Cantrell <dcantrell@redhat.com>

zsh.spec

@@ -1,8 +1,8 @@
 Summary: Powerful interactive shell
 Name: zsh
 Version: 5.9
-Release: 5%{?dist}
-License: MIT
+Release: 6%{?dist}
+License: MIT-Modern-Variant AND ISC AND GPL-2.0-only
 URL: http://zsh.sourceforge.net/
 Source0: https://downloads.sourceforge.net/%{name}/%{name}-%{version}.tar.xz
 Source1: zlogin.rhs
@@ -165,6 +165,9 @@ fi
 %doc Doc/*.html
 
 %changelog
+* Wed May 17 2023 David Cantrell <dcantrell@redhat.com> - 5.9-6
+- Update the License tag to use SPDX identifiers
+
 * Sat Jan 21 2023 Fedora Release Engineering <releng@fedoraproject.org> - 5.9-5
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_38_Mass_Rebuild