chore: Adds test_segment_message to .gitignore (#1026)

Author: mfulb

axiom/tests/.gitignore

@@ -95,6 +95,7 @@ test_segment
 test_segment_children
 test_segment_datastore
 test_segment_external
+test_segment_message
 test_segment_private
 test_segment_terms
 test_segment_traces