Update Vespa version to 8.403.12. (#3356)

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

Author: github-actions[bot]

_config.yml

@@ -88,4 +88,4 @@ defaults:
       index : true
 
 variables:
-  vespa_version: "8.402.27"
+  vespa_version: "8.403.12"