https://github.com/irgeek/StrEnum/issues/39

--- StrEnum-0.4.15/setup.py.orig
+++ StrEnum-0.4.15/setup.py
@@ -28,7 +28,6 @@
         ],
         "release": ["twine"],
     },
-    setup_requires=["pytest-runner"],
     classifiers=[
         "Development Status :: 5 - Production/Stable",
         "Programming Language :: Python :: 3 :: Only",