Resolve "ci: error jobs:release:release description should be a string"

What does this MR do?

According to the docs, release:description is optional, however CI Lint will fail if release:description is not specified.

This MR updates the documentation to show release:description as mandatory to reflect this behavior.

Screenshots (strongly suggested)

Without Description	With Description

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Related to #271565 (closed)