Merge pull request rails#53949 from sikachu/guides-convert-squarebrackets

Convert `[]` in heading to `-squarebrackets` in DOM id

Author: kamipo

guides/rails_guides/markdown.rb

@@ -55,6 +55,7 @@ def dom_id_text(text)
 
         text.downcase.gsub(/\?/, "-questionmark")
                      .gsub(/!/, "-bang")
+                     .gsub(/\[\]/, "-squarebrackets")
                      .gsub(/[#{escaped_chars}]+/, " ").strip
                      .gsub(/\s+/, "-")
       end