Set cached_result=true when there is a cache hit in the execution ser… (

#7967)

…vice

Without this, these cache hits look like executions to bazel. I don't
think it matters to functionality, but it does underreport the cache hit
ratio.

enterprise/server/remote_execution/operation/operation.go

@@ -353,7 +353,9 @@ func PublishOperationDone(stream StreamLike, taskID string, adInstanceDigest *di
 // ExecuteResponseWithCachedResult returns an ExecuteResponse for an action
 // result served from cache.
 func ExecuteResponseWithCachedResult(ar *repb.ActionResult) *repb.ExecuteResponse {
-	return ExecuteResponseWithResult(ar, nil /*=err*/)
+	r := ExecuteResponseWithResult(ar, nil /*=err*/)
+	r.CachedResult = true
+	return r
 }
 
 // ExecuteResponseWithResult returns an ExecuteResponse for an action result