otlptranslator: fix silently swallowed error in addSumNumberDataPoints (#17954)

The createAttributes error was incorrectly returning nil instead of err,
causing errors to be silently discarded. This could lead to silent data
loss for sum metrics during OTLP ingestion.

Fixes #17953

Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>

storage/remote/otlptranslator/prometheusremotewrite/number_data_points.go

@@ -86,7 +86,7 @@ func (c *PrometheusConverter) addSumNumberDataPoints(ctx context.Context, dataPo
 			meta.MetricFamilyName,
 		)
 		if err != nil {
-			return nil
+			return err
 		}
 		var val float64
 		switch pt.ValueType() {