Pin the numpy version v1.23.5

Signed-off-by: Yuki Iwai <yuki.iwai.tz@gmail.com>

Makefile

@@ -169,6 +169,11 @@ prepare-pytest:
 	# REF: https://github.com/kubeflow/katib/pull/2251
 	# TODO (tenzen-y): Once we upgrade libraries depended on typing-extensions==4.5.0, we can remove this line.
 	pip install typing-extensions==4.6.3
+	# This is a workaround to avoid the following error.
+	# AttributeError: module 'numpy' has no attribute 'int'
+	# See more: https://github.com/numpy/numpy/pull/22607
+	# TODO (tenzen-y): Once we remove skopt suggestion service, we can remove this line.
+	numpy==1.23.5
 
 prepare-pytest-testdata:
 ifeq ("$(wildcard $(TEST_TENSORFLOW_EVENT_FILE_PATH))", "")