The MessageQueue._publish ends Otel spans more than ones

[0x6368656174]

A step-by-step description of how to reproduce the issue, based on the linked reproduction.

1. Enable OpenTelemetry by setting enableOpenTelemetryTracing: true in the PubSub constructor
2. Try to send more than one message at the same time
3. See messages like Cannot execute the operation on ended Span {traceId: e60f51b12990ebe1359223f4db06b98e, spanId: 01c61e673f5ed52e} and send e60f51b12990ebe1359223f4db06b98e-01c61e673f5ed52e - You can only call end() on a span once. in the console

A clear and concise description of what the bug is, and what you expected to happen.

The OpenTelemetry span could be ended only once. But MessageQueue._publish method could close rpcSpan and message parent spans more than once if it has more than one message to process, because closing spans is implemented in the loop:

nodejs-pubsub/src/publisher/message-queues.ts

Lines 175 to 180 in 91ebe73

	messages.forEach(m => {
	// We're finished with both the RPC and the whole publish operation,
	// so close out all of the related spans.
	rpcSpan?.end();
	tracing.PubsubEvents.publishEnd(m);
	m.parentSpan?.end();

A clear and concise description WHY you expect this behavior, i.e., was it a recent change, there is documentation that points to this behavior, etc. **

There are no docs describing OpenTelemetry span.end behaviour. However, you could see that it is forbidden in the Otel source code:
https://github.com/open-telemetry/opentelemetry-js/blob/5333204134f71f42c4612735106f83fa8c691102/packages/opentelemetry-sdk-trace-base/src/Span.ts#L267-L272