fix: update_existing logic

[zkoppert]

Pull Request

fixes #208

Proposed Changes

Simplify and correct the handling of the update_existing parameter when checking for existing Dependabot configuration files. The most important changes include removing the update_existing parameter from the check_existing_config function and updating the surrounding logic accordingly. This should result in fixing the situation described in #208. I did have to remove a test now that the update_existing parameter is no longer used in the check_existing_config function.

Readiness Checklist

Author/Contributor

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Reviewer

• Label as either fix, documentation, enhancement, infrastructure, maintenance or breaking

[jmeridth]

LGTM. Nice and simple.