docs: make line bold

Author: kenjis

user_guide_src/source/intro/requirements.rst

@@ -19,7 +19,7 @@ PHP and Required Extensions
 .. warning::
     - The end of life date for PHP 7.4 was November 28, 2022.
     - The end of life date for PHP 8.0 was November 26, 2023.
-    - If you are still using PHP 7.4 or 8.0, you should upgrade immediately.
+    - **If you are still using PHP 7.4 or 8.0, you should upgrade immediately.**
     - The end of life date for PHP 8.1 will be December 31, 2025.
 
 .. note::