Fixed #25558 -- Fixed nondeterministic test failure on Windows: test_clearsessions_command.

The test session without an expiration date added in refs #22938 wasn't
always deleted on Windows because get_expiry_age() returns zero and the
file backend didn't consider that an expired session.

django/contrib/sessions/backends/file.py

@@ -99,7 +99,7 @@ class SessionStore(SessionBase):
 
                 # Remove expired sessions.
                 expiry_age = self.get_expiry_age(expiry=self._expiry_date(session_data))
-                if expiry_age < 0:
+                if expiry_age <= 0:
                     session_data = {}
                     self.delete()
                     self.create()