Fixed design issues in PR template (#834)

Don't generate "mentions" on issue 123 from every PR.

Author: gschaffner

.github/pull_request_template.md

@@ -21,10 +21,12 @@ these instructions.
 ### Updating the changelog
 
 If there are no entries after the last release, use `**UNRELEASED**` as the version.
-If, say, your patch fixes issue #123, the entry should look like this:
+If, say, your patch fixes issue <span>#</span>123, the entry should look like this:
 
-`* Fix big bad boo-boo in task groups (#123
-<https://github.com/agronholm/anyio/issues/123>_; PR by @yourgithubaccount)`
+```
+- Fix big bad boo-boo in task groups
+  (`#123 <https://github.com/agronholm/anyio/issues/123>`_; PR by @yourgithubaccount)
+```
 
 If there's no issue linked, just link to your pull request instead by updating the
 changelog after you've created the PR.