Fix list that doesn't render properly

What does this MR do?

I noticed the list here doesn't render properly: https://docs.gitlab.com/ee/install/docker.html

Related issues

None.

Author's checklist

• Apply the correct labels and milestone
• Port the MR to EE (or backport from CE): always recommended, required when the ee-compat-check job fails

Review checklist

• Your team's review (required)
• PM's review (recommended, but not a blocker)
• Technical writer's review (required)
• Merge the EE-MR first, CE-MR afterwards