Resolve "Markdown header `code` does not have the correct font-size"

app/assets/stylesheets/framework/variables.scss

@@ -233,7 +233,7 @@ $md-area-border: #ddd;
 /*
  * Code
  */
-$code_font_size: 12px;
+$code_font_size: 90%;
 $code_line_height: 1.6;
 /*

changelogs/unreleased/48549-markdown-header-code-does-not-have-the-correct-font-size.yml

+---
+title: fix size of code blocks in headings
+merge_request:
+author:
+type: fixed