Add class to heading

HI everyone. So i read here
that i can add class to a heading. i added settings to config file

defaultMarkdownHandler = "goldmark"
  unsafe = true
  attribute = true

Hugo version is 0.83.1. When i check on github my markdown file, i can see for example,
heading { class=“goBack” }
But if i inspect on website there is no class at all. My colleague couldn’t make it work on his laptop locally too.
Can you help me please, what might be a problem ?

The Markdown syntax for the heading is not quite right. It should be:
## heading ## { class="goBack" }

You are right. i wrote an example in a bad way. This is an actual part of code:
### Developer { class="goBack" }

Check that the quotation marks are NOT typographic but proper ones: ".