Add force-push-detection

[koppor]

Fixes https://github.com/JabRef/jabref-issue-melting-pot/issues/795

Also adds better "line breaks" in Markdown - (Based on the information at https://de.wikipedia.org/wiki/YAML).

Mandatory checks

• I own the copyright of the code submitted and I licence it under the MIT license
• Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

Only comments if all tests ran, Thus, a contributor might add a new commit (without force pushing), which would prevent a comment. But I think, this is better than nothing.

[github-actions]

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