Allow None to be passed to egg_basename

Author: abravalheri

setuptools/command/egg_info.py

@@ -776,11 +776,11 @@ def get_pkg_info_revision():
     return 0
 
 
-def _egg_basename(egg_name, egg_version, py_version=PY_MAJOR, platform=None):
+def _egg_basename(egg_name, egg_version, py_version=None, platform=None):
     """Compute filename of the output egg. Private API."""
     name = _normalization.filename_component(egg_name)
     version = _normalization.filename_component(egg_version)
-    egg = f"{name}-{version}-py{py_version}"
+    egg = f"{name}-{version}-py{py_version or PY_MAJOR}"
     if platform:
         egg += f"-{platform}"
     return egg