Add vitest temp file to gitignore

[lb-]

WHY are these changes introduced?

When running npm run test:watch the file packages/hydrogen-codegen/tsconfig.vitest-temp.json is created each time and should not be committed.

WHAT is this pull request doing?

Ignores any tsconfig.vitest-temp.json files that are created within the repository.

HOW to test your changes?

Run npm run test:watch, confirm that there is no file packages/hydrogen-codegen/tsconfig.vitest-temp.json appearing in unstaged changes.

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes N/A
• I've added tests to cover my changes N/A
• I've added or updated the documentation N/A