fix(ssr): skip updateCjsSsrExternals if legacy flag disabled

[bluwy]

Description

The updateCjsSsrExternals function updates server._ssrExternals that's only used here:

vite/packages/vite/src/node/plugins/importAnalysis.ts

Lines 488 to 493 in 3224a51

	if (config.legacy?.buildSsrCjsExternalHeuristics) {
	if (
	cjsShouldExternalizeForSSR(specifier, server._ssrExternals)
	) {
	return
	}

Since that code only runs on config.legacy?.buildSsrCjsExternalHeuristics: true, we can also add the same guard for updateCjsSsrExternals

Additional context

cc @delucis who found this. It was logging the ... doesn't appear to be written in CJS ... warning unnecessarily.

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[patak-dev]

Interesting we missed this one for so long