fix: entries in ssr.external

[patak-dev]

Fixes #9275

Description

Fixes a regression introduced by:

• fix: ssr.external/noExternal should apply to packageName #9146

Only package names are valid in ssr.noExternal, as #9146 corrected, but ssr.external allows defining package names and also individual entries.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[patak-dev]

vite-ecosystem-ci run: https://github.com/vitejs/vite-ecosystem-ci/actions/runs/2714857134

All green, nuxt is failing because they deleted the vite-3 branch after merging:

• feat(vite)!: upgrade vite to v3 nuxt/framework#5398
  We just moved back to main in vite-ecosystem-ci after this run

I think we can merge and release this one in the next patch to correct the regression