Add LabEx to list of MOOC (#11533)

* Add LabEx to list of free online courses

* Update courses/free-courses-en.md

Co-authored-by: Eric Hellman <eric@hellman.net>

---------

Co-authored-by: huhuhang <no-reply@huhuhang.com>
Co-authored-by: Eric Hellman <eric@hellman.net>

courses/free-courses-en.md

@@ -128,6 +128,7 @@
 * [FutureLearn](https://www.futurelearn.com)
 * [IITBombayX (IITBX)](https://www.iitbombayx.in)
 * [Khan Academy](https://www.khanacademy.org)
+* [LabEx](https://labex.io)
 * [LearnWeb3 DAO \| Become a Web3 Developer for Free](https://learnweb3.io)
 * [MIT OCW](http://ocw.mit.edu)
 * [MOOC.fi](https://www.mooc.fi/en/)