pin vite plugin to next.5 until issues are resolved

[Rich-Harris]

I think we need to pin vite-plugin-svelte to next.5 until the dev-time FOUC is resolved, since it's causing unrelated tests to fail. cc @dominikg

Before submitting the PR, please make sure you do the following

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.

Tests

• Run the tests with pnpm test and lint the project with pnpm lint

Changesets

• If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpx changeset and following the prompts

[dominikg]

the css links in head to SSR'd component styles generated here: https://github.com/sveltejs/kit/blob/master/packages/kit/src/core/dev/index.js#L232..L245
may be causing this issue: #718

vite-plugin-svelte 1.0.0-next.6 changed the vitural css module id format
from Foo.svelte.css?svelte&type=style
to Foo.svelte?svelte&type=style&lang.css
This was done to fix this: sveltejs/vite-plugin-svelte#14

Due to that change kit no longer detects the .css ending and doesn't create a link in head during ssr. That should fix #718 at the expense of fouc on dev.

Not sure why the pipelines in this PR failed so spectacularly, but might i suggest that users can pick their poison via pnpm overrides https://pnpm.io/package_json#pnpmoverrides until we fixed this for good in both cases?

[Rich-Harris]

The pipelines failed because I accidentally moved the package to devDependencies from dependencies, so Rollup tried to bundle it 🤦

[Rich-Harris]

Merging this on a temporary basis, in full acknowledgment that it's not an ideal solution, because it'll make it too hard to work on other stuff if tests keep failing. I had a go at a fix in #1031 but there's a missing piece