React Testing lesson: Recommend setup functions over beforeEach

[Ghoulayush]

…Testing

Because

The current lesson suggests using beforeEach in Vitest for rendering components multiple times in tests. However, React Testing Library (RTL) discourages this practice in favor of using a custom setup function. This PR updates the lesson to align with best practices by recommending setup functions instead of beforeEach .

This PR

• Replaces the sentence:
  "For a lot of tests for a component, the beforeEach Vitest function could prove handy."
  with
  "For a lot of tests for a component, a custom setup function could prove handy."
• Ensures consistency with the RTL documentation and the following lesson.

Issue

Closes #29381

Additional Information

The change aligns with React Testing Library’s official guidance, which discourages rendering components inside beforeEach and recommends using a setup function instead.

Pull Request Requirements

• I have thoroughly read and understand The Odin Project curriculum contributing guide
• The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
• The Because section summarizes the reason for this PR
• The This PR section has a bullet point list describing the changes in this PR
• If this PR addresses an open issue, it is linked in the Issue section
• If any lesson files are included in this PR, they have been previewed with the Markdown preview tool to ensure it is formatted correctly
• If any lesson files are included in this PR, they follow the Layout Style Guide

[Ghoulayush]

Hey @01zulfi , I’ve submitted the PR for #29381. Let me know if any changes are needed. Thanks! 😊

[Ghoulayush]

@gingkapls Thanks for catching that! I've reverted the unintended changes