Fix license header in pre-commit hook

The file was not updated to include the GPL 2.0+ header as well when it
was backported.

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>

tests/git-scripts/pre-commit.sh

@@ -3,7 +3,13 @@
 # pre-commit.sh
 #
 # Copyright The Mbed TLS Contributors
-# SPDX-License-Identifier: Apache-2.0
+# SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+#
+# This file is provided under the Apache License 2.0, or the
+# GNU General Public License v2.0 or later.
+#
+# **********
+# Apache License 2.0:
 #
 # Licensed under the Apache License, Version 2.0 (the "License"); you may
 # not use this file except in compliance with the License.
@@ -16,6 +22,27 @@
 # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+#
+# **********
+#
+# **********
+# GNU General Public License v2.0 or later:
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+# **********
 
 # Purpose
 #