tests: use wal_keep_segments in make_simple_node

Author: gsmolk

tests/helpers/ptrack_helpers.py

@@ -373,6 +373,8 @@ def make_simple_node(
 
         if node.major_version >= 13:
             options['wal_keep_size'] = '200MB'
+        else:
+            options['wal_keep_segments'] = '100'
 
         # set default values
         self.set_auto_conf(node, options)