docs(christmas-shop): fix swapped path segments in rs.school docs link

[kafka2020]

Title of Pull Request

Fix incorrect link in the "christmas-shop" to rs.school private repository docs

🤔 This is a

• 🌟 New task
• 🌐 New module
• ⚙️ Update to an existing task
• 🔧 Update to an existing module
• 🔗 Update or addition of external resources or links
• 🐛 Fix in a task or related content
• 🛠 Fix in a module or related content
• ✏️ Fixed a typo or grammatical error
• 🔗 Fixed a broken link
• ❓ Other (specify: ****____****)

Description

• Brief Overview:
  Fixed an incorrect URL in christmas-shop. The path segments /ru and /docs
  were swapped, causing the link to lead to a non-existent page.
• Implementation Approach:
  Changed the link from /docs/ru/private-repository
  to the correct /docs/private-repository.

Additional Information

• Screenshots/Links:
  Correct link: [https://rs.school/docs/private-repository]
• Related Issues:

Checklist

• ✅ I have performed a self-review of my own code.
• 📝 I have commented my code, particularly in hard-to-understand areas.
• 🔧 I have made corresponding changes to the documentation (if applicable).
• 🚫 My changes generate no new warnings or errors.