Update Vespa version to 8.558.9. (#4019)

Co-authored-by: kkraune <bot+actions@vespa.ai>

Author: github-actions[bot]

_config.yml

@@ -100,4 +100,4 @@ defaults:
       index : true
 
 variables:
-  vespa_version: "8.557.7"
+  vespa_version: "8.558.9"