fix: ensure existing dependabot configs without end of file newlines get processed properly

[zkoppert]

Pull Request

fixes #231

Ensure existing dependabot configs without end of file newlines get processed properly so we can add new language configs without a formatting error. See #231 for details on formatting error.

Proposed Changes

This pull request introduces a new test case to the test_dependabot_file.py file to ensure the dependabot.yml file is built correctly with bundler and specific configurations. It also modifies the existing config builder code to detect existing newlines and handle the case where one doesn't already exist. The goal of all of this is to prevent writing new language configs starting on the same line as the previous config, breaking the yaml format.

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request
• run make lint and fix any issues that you have introduced
• run make test and ensure you have test coverage for the lines you are introducing
• If publishing new data to the public (scorecards, security scan results, code quality results, live dashboards, etc.), please request review from @jeffrey-luszcz

Reviewer

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

[jmeridth]