fix: Update CODEOWNERS parsing to align to Gitlab's official regex

[darylgraham]

🚨 Proposed changes

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The current regex used for parsing CODEOWNERS files does not allow for usernames with a period in them (eg: @code.owner). This change updates the regex used to match the official regex.

Closes #558 #595

⚙️ Types of changes

What types of changes does your code introduce? Put an x in the boxes that apply

• [ ] New feature (non-breaking change which adds functionality)
• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation Update (if none of the other choices apply)
• [ ] Refactor

[darylgraham]

Sorry it took so long, I got swamped and couldn’t get to it.