docs: use GitHub markdown Note

Author: kenjis

contributing/styleguide.md

@@ -200,7 +200,7 @@ conditions MUST always be at the beginning or at the end of the line, not a mix
 - The conditional operator, also known simply as the ternary operator, MUST be preceded and followed by at least one space around both the `?` and `:` characters.
 - When the middle operand of the conditional operator is omitted, the operator MUST follow the same style rules as other binary comparison operators.
 
-**Note:**
+> [!NOTE]
 > All the preceding rules are quoted from PSR-12. You may visit its website to view the code block samples.
 
 ## Custom Conventions

contributing/workflow.md

@@ -240,7 +240,7 @@ are working in.
 At some point, you will decide that your feature branch is complete, or
 that it could benefit from a review by fellow developers.
 
-> **Note**
+> [!NOTE]
 > Remember to sync your local repo with the shared one before pushing!
 It is a lot easier to resolve conflicts at this stage.
 
@@ -279,7 +279,7 @@ Make sure that the PR title is helpful for the maintainers and other
 developers. Add any comments appropriate, for instance asking for
 review.
 
-> **Note**
+> [!NOTE]
 > If you do not provide a title or description for your PR, the odds of it being
 > summarily rejected rise astronomically.