Bump go.opentelemetry.io/otel/sdk in /extension/zpagesextension

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] <[email protected]>

extension/zpagesextension/go.mod

@@ -10,8 +10,8 @@ require (
 	go.opentelemetry.io/collector/confmap v0.89.0
 	go.opentelemetry.io/collector/extension v0.89.0
 	go.opentelemetry.io/contrib/zpages v0.45.0
-	go.opentelemetry.io/otel/sdk v1.20.0
-	go.opentelemetry.io/otel/trace v1.20.0
+	go.opentelemetry.io/otel/sdk v1.21.0
+	go.opentelemetry.io/otel/trace v1.21.0
 	go.uber.org/zap v1.26.0
 )
 
@@ -34,8 +34,8 @@ require (
 	go.opentelemetry.io/collector/featuregate v1.0.0-rcv0018 // indirect
 	go.opentelemetry.io/collector/pdata v1.0.0-rcv0018 // indirect
 	go.opentelemetry.io/collector/service v0.89.0 // indirect
-	go.opentelemetry.io/otel v1.20.0 // indirect
-	go.opentelemetry.io/otel/metric v1.20.0 // indirect
+	go.opentelemetry.io/otel v1.21.0 // indirect
+	go.opentelemetry.io/otel/metric v1.21.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
 	golang.org/x/net v0.17.0 // indirect
 	golang.org/x/sys v0.14.0 // indirect