chore(metrics): fix tests when warnings are disabled (#994)

Author: Michael Brewer

Diff for: tests/functional/test_metrics.py

@@ -552,6 +552,7 @@ def lambda_handler(evt, context):
 
     # THEN it should raise a warning instead of throwing an exception
     with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("default")
         lambda_handler({}, {})
         assert len(w) == 1
         assert str(w[-1].message) == "No metrics to publish, skipping"