Update Vespa version to 8.395.28. (#3321)

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

Author: github-actions[bot]

_config.yml

@@ -83,4 +83,4 @@ defaults:
       index : true
 
 variables:
-  vespa_version: "8.393.3"
+  vespa_version: "8.395.28"