Automigrations: Fix missing support for mts vite config

[drik98]

What I did

When migrating to storybook 8.0.0 using pnpm dlx storybook@latest upgrade one of the migration checks said

🔎 found a 'viteConfigFile' migration:
╭ Migration notification ──────────────────────────────────────────────────────────╮
│                                                                                  │
│   Since version 8.0.0, Storybook no longer ships with a Vite config build-in.    │
│   Please add a vite.config.js file to your project root.                         │
│                                                                                  │
│   You can find more information on how to do this here:                          │
│   https://storybook.js.org/docs/8.0/migration-guide/#missing-viteconfigjs-file   │
│                                                                                  │
│   This change was necessary to support newer versions of Vite.                   │
│                                                                                  │
╰──────────────────────────────────────────────────────────────────────────────────╯

which is wrong because my project does have a vite config file (vite.config.mts) just with a different ending then expected from storybook. Storybook already supports both .mjs and .ts so I just added .mts as well as it is already working even though the message says it does not.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

Already worked for me locally anyway.

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

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[valentinpalkovic]

LGTM! Thank you @drik98 for your contribution!

[drik98]

@valentinpalkovic Will this be merged?

[valentinpalkovic]

@drik98 Thank you for the heads up! Merging in progress...