Up to date Flutter Bangla course resource (#9491)

* feat: flutter course by Rabbil hasan resource  added

* Update free-courses-bn.md

* Update courses/free-courses-bn.md

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

---------

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

courses/free-courses-bn.md

@@ -91,6 +91,7 @@ Shikkhangon BD
 ### Flutter
 
 * [Flutter Bangla Tutorial](https://www.youtube.com/playlist?list=PLg87mxEuu8-692INeEsxudyVifz7M3efy) - Techno BD XYZ
+* [Flutter Tutorial Bangla](https://www.youtube.com/playlist?list=PLkyGuIcLcmx3-Z3QML9xkYZtdKh91LeYC) - Rabbil Hasan
 * [Flutter Tutorial Bangla](https://www.youtube.com/playlist?list=PLZJlOXxGEkuyZQ-vA7B5vpvvtWU3Upo6p) - Soykot Hosen