test(node-core): Proof that withMonitor doesn't create a new trace

[JPeer264]

In #18029 the expectation is that the withMonitor is creating a new trace. Currently it is not reflected in the docs what is expected when withMonitor is executed. This test proofs that this is the case.

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	9,086	-	8,737	+4%
GET With Sentry	1,360	15%	1,353	+1%
GET With Sentry (error only)	6,034	66%	6,020	+0%
POST Baseline	1,197	-	1,196	+0%
POST With Sentry	508	42%	505	+1%
POST With Sentry (error only)	1,064	89%	1,049	+1%
MYSQL Baseline	3,297	-	3,278	+1%
MYSQL With Sentry	409	12%	489	-16%
MYSQL With Sentry (error only)	2,707	82%	2,685	+1%

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