Draft: replace defer with t.Cleanup in tests

What does this MR do?

I am planning to solve this issue in at least 2 MR's. This MR specifically focuses on acceptance tests. I have changed the code so that all Body's will be closed using testhelpers.Close() function. I have managed to pass all the tests on local but somehow, pipeline has failed. You can see the error "testhelpers.Close is undefined" which is kind of weird because I have imported gitlab.com/gitlab-org/gitlab-pages/internal/testhelpers on all the necessary files. I also marked this MR as 'Draft' because I need to implement unit tests as well. So I need your review.

Related to #607 (closed)

TODO

• I added the Changelog trailer (e.g. Changelog: added) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines