fix: externalize workspace relative import when bundle config

[bluwy]

Description

Fixes failing sveltekit test in ecosystem-ci.

Additional context

The issue is that in this config file. It's importing ../../utils.js, which imports from another workspace package (kit). If we bundle the files and leave bare imports externalized, the bundled code can't import deps from that other workspace package, leading to a runtime error.

This PR makes sure that for files in another package, we should externalize them so that they can require the deps themselves. However, this may regress the second workaround for #5370 if the file from another package doesn't import anything, but I don't think that it's good to allow it in the first place (?).

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

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