chore(python): Rename parameter

Author: sentrivana

docs/platforms/python/migration/2.x-to-3.x.mdx

@@ -81,7 +81,7 @@ Tracing in the Sentry Python SDK `3.x` is powered by [OpenTelemetry](https://ope
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-Any spans without a parent span will become transactions by default. If you want to avoid promoting a span without a parent to a transaction, you can pass the `only_if_parent=True` keyword argument to `sentry_sdk.start_span()`.
+Any spans without a parent span will become transactions by default. If you want to avoid promoting a span without a parent to a transaction, you can pass the `only_as_child_span=True` keyword argument to `sentry_sdk.start_span()`.
 
 `sentry_sdk.start_transaction()` and `sentry_sdk.start_span()` no longer take the following arguments: `trace_id`, `baggage`, `span_id`, `parent_span_id`, `custom_sampling_context` (see below). Use `sentry_sdk.continue_trace()` for propagating trace data.