Add missed license header to test_exp.py

Author: ndgrigorian

dpctl/tests/elementwise/test_exp.py

@@ -1,3 +1,19 @@
+#                       Data Parallel Control (dpctl)
+#
+#  Copyright 2020-2024 Intel Corporation
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
 import itertools
 
 import numpy as np