chore(appsec): track_user must use tag the service_entry_span (#14384)

## Description

This is an omission from PR: #14210 . The `track_user` function must
pass to tag the user on to the `set_user` helper.

## Checklist
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[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
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[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Author: florentinl

ddtrace/appsec/track_user_sdk.py

@@ -104,6 +104,7 @@ def track_user(
         scope=usr_scope if isinstance(usr_scope, str) else None,
         role=usr_role if isinstance(usr_role, str) else None,
         session_id=session_id,
+        span=span,
         may_block=_auto,
         mode=_constants.LOGIN_EVENTS_MODE.AUTO if _auto else _constants.LOGIN_EVENTS_MODE.SDK,
     )