Parsing a document containing <button type="submit" class="btn btn-outline-secondary rounded-right" type="button">Test</button> produces a DOM element with a type attribute set to button.
However, the HTML specification explicitly says that duplicate attributes must be ignored: https://html.spec.whatwg.org/multipage/parsing.html#parse-error-duplicate-attribute This means that the first one should win, giving a type of submit.

See symfony/symfony#52889 for the original report