CloudWatch Logs: Queries in an expression should run synchronously (#64443)

pkg/expr/nodes.go

@@ -21,6 +21,8 @@ var (
 	logger = log.New("expr")
 )
 
+const FromExpressionHeaderName = "FromExpression"
+
 type QueryError struct {
 	RefID string
 	Err   error
@@ -227,6 +229,7 @@ func (dn *DSNode) Execute(ctx context.Context, now time.Time, _ mathexp.Vars, s
 		},
 		Headers: dn.request.Headers,
 	}
+	req.Headers[FromExpressionHeaderName] = "true"
 
 	responseType := "unknown"
 	defer func() {