add practice-linux-commands-free-course to courses/free-courses-en.md (#11524)

* add practice-linux-commands-free-course

* Update free-courses-en.md: Remove duplicate Linux commands course

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Co-authored-by: huhuhang <[email protected]>

Author: huhuhang

Diff for: more/free-programming-interactive-tutorials-en.md

@@ -298,6 +298,7 @@
 * [Learning operating system development using Linux kernel and Raspberry Pi](https://github.com/s-matyukevich/raspberry-pi-os) - Sergey Matyukevich *(:construction: in process)*
 * [Linux Journey - Fun and Easy](https://linuxjourney.com) - Cindy Quach
 * [Operating System Tutorial](https://www.scaler.com/topics/operating-system/) - Scaler Topics
+* [Practice Linux Commands (Hands-On Labs)](https://labex.io/tutorials/practice-linux-commands-free-tutorials-398420) - LabEx
 * [Project eXpOS: eXperimental Operating System](https://exposnitc.github.io) - Murali Krishnan K., Department of Computer Science and Engineering of the Calicut National Institute of Technology (HTML)