fix: More Node v18 issues

[timfish]

This PR fixes another usage of tracingChannel which isn't supported in Node v18.0.0.

I also added a test to ensure we don't break this again at import time.

[sentry]

Bug: The change to a namespace import introduces a runtime TypeError on Node.js <18.19.0 when mysqlChannelIntegration is used, as diagnosticsChannel.tracingChannel will be undefined.
_{Severity: MEDIUM}

Suggested Fix

Add a runtime check to ensure diagnosticsChannel.tracingChannel is a function before calling it. This will prevent the TypeError on older Node.js versions where the API does not exist, effectively guarding the integration's setup.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: packages/server-utils/src/integrations/tracing-channel/mysql.ts#L76

Potential issue: The change from a named import to a namespace import (`import * as
diagnosticsChannel`) prevents a load-time crash on Node.js versions below 18.19.0.
However, it introduces a new runtime bug. On these older Node versions,
`diagnosticsChannel.tracingChannel` is `undefined`. When the `mysqlChannelIntegration`
is initialized, its `setupOnce()` method is called, which attempts to execute
`diagnosticsChannel.tracingChannel(...)`. This results in a `TypeError:
diagnosticsChannel.tracingChannel is not a function`, crashing the application at
runtime during SDK initialization.

Also affects:

• packages/node-core/src/integrations/pino.ts:130
• packages/opentelemetry/src/tracingChannel.ts:56

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[andreiborza]

Good idea putting this on ci!