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	11,468	-	8,786	+31%
GET With Sentry	1,647	14%	1,286	+28%
GET With Sentry (error only)	7,618	66%	6,012	+27%
POST Baseline	1,165	-	1,157	+1%
POST With Sentry	527	45%	470	+12%
POST With Sentry (error only)	1,036	89%	1,009	+3%
MYSQL Baseline	3,998	-	3,242	+23%
MYSQL With Sentry	517	13%	391	+32%
MYSQL With Sentry (error only)	3,281	82%	2,614	+26%

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