fix setuptools deprecation (#880)

Signed-off-by: mosfet80 <[email protected]>

Author: mosfet80

rosidl_pycommon/setup.py

@@ -20,7 +20,11 @@
     maintainer_email='[email protected], [email protected], [email protected], [email protected]',  # noqa: E501
     description='Common Python functions used by rosidl packages.',
     license='Apache License, Version 2.0',
-    tests_require=['pytest'],
+    extras_require={
+        'test': [
+            'pytest',
+        ],
+    },
     entry_points={
         'console_scripts': [
         ],