Bump go.opentelemetry.io/otel/sdk from 1.20.0 to 1.21.0 in /exporter

Bumps [go.opentelemetry.io/otel/sdk](https://github.com/open-telemetry/opentelemetry-go) from 1.20.0 to 1.21.0.
- [Release notes](https://github.com/open-telemetry/opentelemetry-go/releases)
- [Changelog](https://github.com/open-telemetry/opentelemetry-go/blob/main/CHANGELOG.md)
- [Commits](open-telemetry/opentelemetry-go@v1.20.0...v1.21.0)

---
updated-dependencies:
- dependency-name: go.opentelemetry.io/otel/sdk
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

exporter/go.mod

@@ -14,10 +14,10 @@ require (
 	go.opentelemetry.io/collector/featuregate v1.0.0-rcv0018
 	go.opentelemetry.io/collector/pdata v1.0.0-rcv0018
 	go.opentelemetry.io/collector/receiver v0.89.0
-	go.opentelemetry.io/otel v1.20.0
-	go.opentelemetry.io/otel/metric v1.20.0
-	go.opentelemetry.io/otel/sdk v1.20.0
-	go.opentelemetry.io/otel/trace v1.20.0
+	go.opentelemetry.io/otel v1.21.0
+	go.opentelemetry.io/otel/metric v1.21.0
+	go.opentelemetry.io/otel/sdk v1.21.0
+	go.opentelemetry.io/otel/trace v1.21.0
 	go.uber.org/multierr v1.11.0
 	go.uber.org/zap v1.26.0
 	golang.org/x/sys v0.14.0