Improve > handling in blockquote in Markdown (#19802)

Co-authored-by: codex <codex@openai.com>
Co-authored-by: fisker Cheung <lionkay@gmail.com>
Co-authored-by: fisker <lionkay@gmail.com>

changelog_unreleased/markdown/19802.md

@@ -0,0 +1,13 @@
+#### Fix Markdown blockquote containing `>` characters (#19802 by @seiyab)
+
+<!-- prettier-ignore -->
+```md
+<!-- Input -->
+> **test**\>
+
+<!-- Prettier stable -->
+> **test**>\>
+
+<!-- Prettier main -->
+> **test**\>
+```