Tweak markdown page to fix rendering

What does this MR do?

While checking this page in GitLab I noticed that things were not being highlighted as expected, looks like the usage of backticks was causing some edge case bugs, so this makes a few adjustments to avoid the issues.

Example: https://gitlab.com/gitlab-org/gitlab/-/blob/4d6a517c1681ffa8e10763e70f5160b84701dfbb/doc/user/markdown.md?page=2#L1044 (all red due to renderer thinking it's all backticked code).

Related issues

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