Golang Queue Docs Reference `StartSpan` which should be `StartChild`

### SDK

Go SDK

### Description

The documentation references `StartSpan` on transactions. However, the SDK uses `StartChild` and doesn't pass the context.

- https://docs.sentry.io/platforms/go/tracing/instrumentation/custom-instrumentation/queues-module/#consumer-instrumentation
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### Suggested Solution

Replace `StartSpan(ctx, opName)` with `StartChild(opName)`