Remove an unnecessary line break for PULL_REQUEST_TEMPLATE.md

This is a trivial change.

Unnecessary line breaks are not made when displaying as a Markdown resource.
https://github.com/rubocop-hq/rubocop/blob/v0.72.0/.github/PULL_REQUEST_TEMPLATE.md

However, unnecessary line breaks are added when opening and opened PR pages.
e.g. #7203

This PR removes an unnecessary line break from confirmation items
when opening a PR.

.github/PULL_REQUEST_TEMPLATE.md

@@ -11,8 +11,7 @@ Before submitting the PR make sure the following are checked:
 * [ ] Squashed related commits together.
 * [ ] Added tests.
 * [ ] Added an entry to the [Changelog](https://github.com/rubocop-hq/rubocop/blob/master/CHANGELOG.md) if the new code introduces user-observable changes. See [changelog entry format](https://github.com/rubocop-hq/rubocop/blob/master/CONTRIBUTING.md#changelog-entry-format).
-* [ ] The PR relates to *only* one subject with a clear title
-  and description in grammatically correct, complete sentences.
+* [ ] The PR relates to *only* one subject with a clear title and description in grammatically correct, complete sentences.
 * [ ] Run `bundle exec rake default`. It executes all tests and RuboCop for itself, and generates the documentation.
 
 [1]: https://chris.beams.io/posts/git-commit/