Fix AuthorListParser#parse for two authors with comma

[koppor]

While reading #8652, I found that ebook.de returns an "OKish" BibTeX:

https://www.ebook.de/de/tools/isbn2bibtex?isbn=9783110702125

@book{9783110702125,
  Author = {Hans-Joachim Habermann, Frank Leymann},
  Title = {Repository},
  Publisher = {Gruyter, Walter de GmbH},
  Year = {2020},
  Date = {2020-10-12},
  PageTotal = {294 Seiten},
  EAN = {9783110702125},
  URL = {https://www.ebook.de/de/product/41373251/hans_joachim_habermann_frank_leymann_repository.html}
}

We convert that to "good" BibTeX by using https://github.com/JabRef/jabref/blob/main/src/main/java/org/jabref/logic/importer/AuthorListParser.java. This code, however, did not work in the special case of two authors. I added a new heuristics for that case and added more test cases for that.

In the concrete case, {Hans-Joachim Habermann, Frank Leymann} needs to be converted to {Habermann, Hans-Joachim AND Leymann, Frank}

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• 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.

[Siedlerchr]

org.jabref.model.entry.AuthorListTest

Test correctNamesWithOneComma() FAILED

[calixtus]

That sounds like English with a french accent to my inner voice...

[Siedlerchr]

I close this for the moment, until we find time to improve the algorithm