fix: swap out raw HTML syntax for semantic/idiomatic markdown (#35917)

Per this: https://www.freecodecamp.org/forum/t/forum-suggestion-unformatted-code-warning/134857/24

`<code>` tags are not the semantically/idiomatically correct way to format code on Discourse. For example, `<code><span></span></code>` renders as that exact HTML, when the intention was almost certainly to render `<code>&lt;span&gt;&lt;/span&gt;</code>` instead.

client/src/templates/Challenges/redux/create-question-epic.js

@@ -49,9 +49,9 @@ function createQuestionEpic(action$, state$, { window }) {
         '**Your code so far**\n',
         filesToMarkdown(files),
         '**Your browser information:**\n\n',
-        'User Agent is: <code>',
+        'User Agent is: `',
         userAgent,
-        '</code>.\n\n',
+        '`.\n\n',
         '**Challenge:**\n',
         challengeTitle,
         '\n**Link to the challenge:**\n',