Add test cases for RTL/LTR linter in English and Arabic book lists

Add sample entries to free-programming-books-en.md and free-programming-books-ar.md to test the RTL/LTR Markdown linter.
These test cases include various combinations of RTL and LTR text, keywords, symbols, and metadata to verify that the linter correctly detects directionality issues and outputs the expected logs and annotations.

Author: gabriele-ciccotelli

books/free-programming-books-ar.md

@@ -41,11 +41,13 @@
 
 * [التحريك عبر CSS‏](https://academy.hsoub.com/files/14-التحريك-عبر-css/) - Donovan Hutchinson, Mohamed Beghat‏ (PDF)
 * [نحو فهم أعمق لتقنيات HTML5‏](https://academy.hsoub.com/files/13-نحو-فهم-أعمق-لتقنيات-html5/) - Mark Pilgrim, Abdullatif Eymash‏ (PDF)
+* [تعلم HTML](https://example.com/html-arabic) - مؤلف تجريبي (PDF)
 
 
 ### Introduction to Programming in Arabic
 
 * [مختصر دليل لغات البرمجة](https://alyassen.github.io/Brief-guide-to-programming-languages-v1.2.4.pdf) - Ali Al-Yassen‏ (PDF)
+* [تعلم C#](https://example.com/csharp-arabic) - مؤلف تجريبي (PDF)
 
 
 ### JavaScript
@@ -80,7 +82,7 @@
 ### Python
 
 * [البرمجة بلغة بايثون](https://academy.hsoub.com/files/15-البرمجة-بلغة-بايثون/)
-
+* [Learn Python](https://example.com/learn-python) - Test Author (PDF)
 
 ### Raspberry Pi
 
@@ -96,6 +98,7 @@
 
 * [تأمين الشبكات اللاسلكية للمستخدم المنزلي](https://mohamedation.com/securing-wifi/ar/) - Mohamed Adel‏ (HTML)
 * [دليل الأمان الرقمي](https://academy.hsoub.com/files/20-%D8%AF%D9%84%D9%8A%D9%84-%D8%A7%D9%84%D8%A3%D9%85%D8%A7%D9%86-%D8%A7%D9%84%D8%B1%D9%82%D9%85%D9%8A/)
+* [كتاب جديد](https://example.com/new-book) - أحمد علي (PDF, HTML)
 
 
 ### SQL

books/free-programming-books-en.md

@@ -8,3 +8,7 @@
 * [English, By Programming Language](free-programming-books-langs.md)
 * [English, By Subject](free-programming-books-subjects.md)
   (The list of books in English is here for historical reasons.)
+* [Learn Python](https://example.com/learn-python) - Test Author (PDF)
+* [تعلم HTML](https://example.com/html-arabic) - مؤلف تجريبي (PDF)
+* [Learn C#](https://example.com/learn-csharp) - John Doe (PDF)
+* [كتاب جديد](https://example.com/new-book) - أحمد علي (PDF, HTML)