Docs: fixes blockquotes syntax

What does this MR do?

Fixes blockquotes syntax.

Related issues

https://gitlab.com/gitlab-com/gitlab-docs/issues/285

Author's checklist

• Apply the correct labels and milestone
• Correctly apply the product badges and tiers
• Port the MR to EE (or backport from CE): https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8738

Review checklist

• Technical writer's review (required)
• Merge the EE-MR first (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8738), CE-MR afterwards

@eread assigning to you as you'll prob can merge this before @axil 😉