BUG: Push rules are not respected on fast-forward merge

Summary

Push rules (commit messages regex) are not respected on fast-forward merge.

Steps to reproduce

• Create a new repository
• Add a regex push rule (Settings/Repository/Push Rules)
• Select fast-forward merge (Setting/General/Merge Request/Merge Method)
• Fork your repository (The push rule is not propagated)
• Make a merge request with a bad commit message
• Approve the Merge request

What is the current bug behavior?

Commit that are not respecting the push rule are allowed

What is the expected correct behavior?

Commit that are not respecting the push rule are not allowed