fix: Use Markdown instead of HTML markup for H3 & H4 headings (#6689)

* fix: Markdown markup for `C++` heading

* fix: Markdown markup for `Дизайн и Aрхитектура` heading

* fix: Markdown H4 markup for `Next.js` heading

* fix: Markdown H3 markup for `C#` heading

courses/free-courses-ar.md

@@ -4,7 +4,7 @@
 * [Assembly](#assembly)
 * [Bootstrap](#bootstrap)
 * [C](#c)
-* [C Sharp](#c-sharp)
+* [C#](#csharp)
 * [C++](#cpp)
 * [Computer Architecture](#computer-architecture)
 * [Dart](#dart)
@@ -66,7 +66,7 @@
 * [Introduction to Programming ( C Language - مقدمة في البرمجة ( لغة السي](https://www.youtube.com/playlist?list=PLMm8EjqH1EFXI8wByY0umF_DQON2S9uws) - Ahmed Sallam
 
 
-### C Sharp
+### <a name="csharp"></a>C\#
 
 * [C#](https://www.youtube.com/playlist?list=PLltZRmsFXWnIfLM0BKgJNZYVnvCDZNAh_) - 6wrni
 * [C# Programming Course Level 1 Basics By Arabic](https://www.youtube.com/playlist?list=PLnzqK5HvcpwQLsXXXxx_mX3WvUEgGM0iA) - محمد شوشان
@@ -74,7 +74,7 @@
 * [Unit Testing in C# [Arabic]](https://www.youtube.com/playlist?list=PLwj1YcMhLRN28xijrXMO255JHsO3csus-) - خالد السعداني
 
 
-<h3 id="cpp">C++</h3>
+### <a name="cpp"></a>C++
 
 * [Arabic C++ For kids & beginners (برمجة لصغار السن والمبتدئيين)](https://www.youtube.com/playlist?list=PLPt2dINI2MIbwnEoeHZnUHeUHjTd8x4F3) - Arabic Competitive Programming
 * [C++ Intensive - برمجة الحاسوب](https://www.youtube.com/playlist?list=PLPt2dINI2MIZPFq6HyUB1Uhxdh1UDnZMS) - Arabic Competitive Programming