ref(core): Adjust MCP server error event mechanism

[Lms24]

This PR adjusts the mechanism type we set to be in line with the trace origin naming scheme.

ref #17212

[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	8,727	-	9,615	-9%
GET With Sentry	1,250	14%	1,278	-2%
GET With Sentry (error only)	5,851	67%	6,177	-5%
POST Baseline	1,191	-	1,218	-2%
POST With Sentry	477	40%	485	-2%
POST With Sentry (error only)	1,038	87%	1,081	-4%
MYSQL Baseline	3,230	-	3,375	-4%
MYSQL With Sentry	412	13%	466	-12%
MYSQL With Sentry (error only)	2,651	82%	2,735	-3%

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