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

more/free-programming-cheatsheets.md

@@ -4,7 +4,7 @@
 * [Artificial Intelligence](#artificial-intelligence)
 * [Bash](#bash)
 * [C](#c)
-* [C#](#c-sharp)
+* [C#](#csharp)
 * [C++](#cpp)
 * [Clojure](#clojure)
 * [Data Science](#data-science)
@@ -63,7 +63,7 @@
 * [The C Cheat Sheet: An Introduction to Programming in C](https://sites.ualberta.ca/~ygu/courses/geoph624/codes/C.CheatSheet.pdf) - Andrew Sterian (PDF)
 
 
-### <a name="c-sharp"></a>C#
+### <a name="csharp"></a>C\#
 
 * [C# Cheat Sheet](https://simplecheatsheet.com/tag/c-cheat-sheet-1/) - Simple Cheat Sheet (HTML)