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-pt_BR.md

@@ -2,7 +2,7 @@
 
 * [Android](#android)
 * [C](#c)
-* [C Sharp](#c-sharp)
+* [C#](#csharp)
 * [C++](#cpp)
 * [CSS](#css)
 * [Dart](#dart)
@@ -55,7 +55,7 @@
 * [Programação Moderna em C](https://www.youtube.com/playlist?list=PLIfZMtpPYFP5qaS2RFQxcNVkmJLGQwyKE) - Papo Binário (Youtube)
 
 
-### C Sharp
+### <a name="csharp"></a>C\#
 
 * [C# e Windows Forms: Consultar CEP no WebService dos Correios](https://www.udemy.com/webservice-correios/) - Gilseone Moraes, Training4All Cursos (Udemy)
 * [C# e Windows Forms: Encurtando URLs com a API do Bitly](https://www.udemy.com/bitly-api/) - Gilseone Moraes, Training4All Cursos (Udemy)
@@ -65,7 +65,7 @@
 * [Manipulando Listas Genéricas em C#](https://www.udemy.com/listas-genericas-em-csharp/) - Gilseone Moraes, Training4All Cursos (Udemy)
 
 
-<h3 id="cpp">C++</h3>
+### <a name="cpp"></a>C++
 
 * [Curso de C++ - A linguagem de programação fundamental para quem quer ser um programador](https://www.youtube.com/playlist?list=PLx4x_zx8csUjczg1qPHavU1vw1IkBcm40) - Canal Fessor Bruno (CFBCursos)