fix(pubsub): move start span logic for publish batch

[duongcongtoai]

Fix: #11186

Having this span started while tracing is disabled do not directly cause memory leak, but if otel sdk is used together with other sdk such as sentry (which internally store a global map of otel span ID -> sentry span ID), if the span never ends the entries in this map is never GCed, and thus all the span object that they refers to never get GCed

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[conventional-commit-lint-gcf]

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