fix: rename CLOCK_SKEW and separate client/server user case (#863)

* fix: rename CLOCK_SKEW and separate client/server user case

* update clock skew to 20s
diff --git a/tests/test_downscoped.py b/tests/test_downscoped.py
index 795ec29..9ca95f5 100644
--- a/tests/test_downscoped.py
+++ b/tests/test_downscoped.py
@@ -669,7 +669,9 @@
         # Set the expiration to one second more than now plus the clock skew
         # accommodation. These credentials should be valid.
         credentials.expiry = (
-            datetime.datetime.min + _helpers.CLOCK_SKEW + datetime.timedelta(seconds=1)
+            datetime.datetime.min
+            + _helpers.REFRESH_THRESHOLD
+            + datetime.timedelta(seconds=1)
         )
 
         assert credentials.valid