When a Sentry-Trace header is sent erroneously multiple times

[wmak]

How do you use Sentry?

Sentry Saas (sentry.io)

Version

latest

Steps to Reproduce

1. Set the sentry-trace header when already in a transaction to a python server
2. The set header will then be read by the server into something like: Sentry-Trace:efa64e95faf54da59b81cce3fb159825-b8efba9273e7a14f-1,efa64e95faf54da59b81cce3fb159825-b8ffba9273e7a14f-1
3. Then when the sdk tries to parse this to get the trace_id it fails

Expected Result

The SDK shouldn't fail to parse the header, and instead should probably(?) just pull the first one or one at random

Actual Result

The regex here

sentry-python/sentry_sdk/tracing_utils.py

Lines 47 to 53 in 171aa16

	SENTRY_TRACE_REGEX = re.compile(
	"^[ \t]*" # whitespace
	"([0-9a-f]{32})?" # trace_id
	"-?([0-9a-f]{16})?" # span_id
	"-?([01])?" # sampled
	"[ \t]*$" # whitespace
	)

fails to parse since the header value now contains a comma unexpectedly

[linear-code]

PY-2571