Add linux upskill challenge link (#4554)

devops-roadmap-ubuntu-linux-upskill-challenge link fixed
fix : #4550

src/data/roadmaps/devops/content/101-operating-systems/linux/100-ubuntu.md

@@ -11,6 +11,6 @@ Visit the following resources to learn more:
 - [Learn the ways of Linux-fu, for free](https://linuxjourney.com/)
 - [Linux Operating System - Crash Course for Beginners](https://www.youtube.com/watch?v=ROjZy1WbCIA)
 - [The Linux Command Line by William Shotts](https://linuxcommand.org/tlcl.php)
-- [r/linuxupskillchallenge](https://www.reddit.com/r/linuxupskillchallenge/)
+- [Linux Upskill Challenge](https://linuxupskillchallenge.org/)
 - [Introduction to Linux - Full Course for Beginners](https://www.youtube.com/watch?v=sWbUDq4S6Y8&pp=ygUTVWJ1bnR1IGNyYXNoIGNvdXJzZQ%3D%3D)
 - [Linux Fundamentals](https://academy.hackthebox.com/course/preview/linux-fundamentals)