style(oxlint/plugins): update oxfmt config to only format plugins in oxlint fixtures

[lilnasy]

• Follow up to style(oxlint/plugins): format test fixtures #15600 and style(linter/plugins): update oxfmt config to format oxlint fixtures #15601.
• Makes the inclusion of the fixtures more specific to only target the plugin files.
• The intention is to prevent autofix CI formatting lintable files and autobreaking assertions in the process.

[Copilot]

Pull Request Overview

This PR refines the formatting configuration to prevent CI auto-formatting from breaking test assertions in fixture files. Previously, all files under apps/oxlint/test/fixtures/ were included for formatting; now only files specifically named plugin.ts are formatted.

Key Changes

• Modified the ignore pattern from including all fixture files to only including plugin.ts files
• This prevents test input files (which may intentionally contain linting errors) from being auto-formatted

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[overlookmotel]

Personally, I like formatting everything that can be formatted. We can use // prettier-ignore comments on parts of files where whitespace etc matters.

Unless this is going to be a major ball-ache for token APIs?

[lilnasy]

This doesn't uniquely affect token APIs. Edit: maybe I spoke too soon. I imagine there will be more cases like this: #15861 (comment).

I was thrown off by the autofix CI autobreaking already written tests. I'll add // prettier-ignore for now and refactor the assertions at a later point.

[overlookmotel]

I don't know what editor you use. I use VS Code, and have installed the Oxc VS Code extension, with "experimental format" and "format on save" options enabled. That's quite useful for this, as when editing fixture files, you see immediately if the file is going to get formatted in a way that you don't want, and it's obvious where to put the // prettier-ignore comments.

But Oxfmt is alpha, so completely understand if you don't want to use it.

Prettier doesn't support a // prettier-ignore-file comment to skip formatting on whole file, so currently Oxfmt doesn't support it either. But we can request that feature (seems useful to me), and that'd make all this rather easier.