[CI] Fix windows image prefix in the new integration pipeline (#6019)

Author: pazone

.buildkite/bk.integration.pipeline.yml

@@ -46,7 +46,7 @@ steps:
         agents:
           provider: "gcp"
           machineType: "n1-standard-8"
-          image: "platform-ingest-elastic-agent-windows-2022"
+          image: "family/platform-ingest-elastic-agent-windows-2022"
         matrix:
           - default
           - fleet