Add mappings on ModsImporter.java

[berry120]

Fixes #9185

• 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]

Thank you for your contribution. Looks good already. Can you please add a test for this as well?
Have a look at the mods importer test files

[berry120]

@Siedlerchr Absolutely, that's now added 👍

[Siedlerchr]

Thanks! Please add a changelog entry, then it's ready!

[berry120]

@Siedlerchr Thanks, done!

[calixtus]

Don't know if this will be accepted to hactoberfest, since the PR was created on 9/30 and they say that they only accepted PRs created between 1 and 31 of october. But we can try anyway.