Avoid pkg_resources import at the top-level.

changelog/4768.trivial.rst

@@ -0,0 +1 @@
+Avoid pkg_resources import at the top-level.

src/_pytest/config/__init__.py

@@ -14,7 +14,6 @@ import warnings
 
 import py
 import six
-from pkg_resources import parse_version
 from pluggy import HookimplMarker
 from pluggy import HookspecMarker
 from pluggy import PluginManager
@@ -815,6 +814,7 @@ class Config(object):
 
     def _checkversion(self):
         import pytest
+        from pkg_resources import parse_version
 
         minver = self.inicfg.get("minversion", None)
         if minver: