Cover subject starting with space

What does this MR do and why?

Describe in detail what your merge request does and why.

Add a check for the commit subject to not start with a space.

The error we show now is The subject must start with a capital letter https://gitlab.com/gitlab-org/gitlab/-/jobs/3218411002

This would give an improved error message

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.