Fixed Markdown In Bangla Books List (#6621)

* Fixed Markdown

* Update free-programming-books-bn.md

* Update free-programming-books-bn.md

* Update books/free-programming-books-bn.md

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

* fix: C++ heading anchor without hash

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

books/free-programming-books-bn.md

@@ -5,7 +5,7 @@
 * [Bootstrap](#bootstrap)
 * [C](#c)
 * [C Sharp](#c-sharp)
-* [C++](#c-1)
+* [C++](#cpp)
 * [Competitive Programming](#competitive-programming)
 * [CSS](#css)
 * [Dart](#dart)
@@ -53,7 +53,7 @@
 * [Pattern Printing in C](https://www.youtube.com/playlist?list=PLgH5QX0i9K3oTxQhx2kejYmQn6qtRULCD) - Anisul Islam
 
 
-<h3 id="cpp">C++</h3>
+### <a name="cpp"></a>C++
 
 * [C++ Bangla Tutorial Course](https://www.youtube.com/playlist?list=PLgH5QX0i9K3q0ZKeXtF--CZ0PdH1sSbYL) - Anisul Islam