Only add commit prefix if branch name matches regex pattern

[Promytheos]

• PR Description Currently if a branch name does not match a regex pattern defined in the config.yaml (commitPrefix/es) the commit message box is populated with the branch name as is - this does not match expectations. A prefix should only be added if there is a match on the regex pattern.

This PR seeks to change that by checking for a match before calling ReplaceAllString - see Issue #3695

• Please check if the PR fulfills these requirements

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• [x] Tests have been added/updated (see here for the integration test guide)
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• [x] You've read through your own file changes for silly mistakes etc