fix(dev): fix CSS import warnings in unstable_dev

[markdalgleish]

Closes #6502

I verified this by running it against the library mentioned in the linked issue.

@pcattori I remember you mentioning that this area will get some more attention, but just raising a quick fix for now in case we want to ship this in the meantime.

[changeset-bot]

🦋 Changeset detected

Latest commit: 7d8b792

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 18 packages

Name	Type
@remix-run/dev	Patch
create-remix	Patch
@remix-run/css-bundle	Patch
remix	Patch
@remix-run/architect	Patch
@remix-run/cloudflare	Patch
@remix-run/cloudflare-pages	Patch
@remix-run/cloudflare-workers	Patch
@remix-run/deno	Patch
@remix-run/eslint-config	Patch
@remix-run/express	Patch
@remix-run/netlify	Patch
@remix-run/node	Patch
@remix-run/react	Patch
@remix-run/serve	Patch
@remix-run/server-runtime	Patch
@remix-run/testing	Patch
@remix-run/vercel	Patch

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[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-70cc627-20230602 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

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[github-actions]

🤖 Hello there,

We just published version 1.17.0-pre.0 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

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[github-actions]

🤖 Hello there,

We just published version 1.17.0 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!