Fix casing "macOS" and "JabRef", vendor: JabRef e.V.

[koppor]

Lightweight alternative to #10345. "Just" fixing the names in our build script (display only)

Moreover, have "JabRef e.V." as vendor and JabRef as mac-package-identifier (instead of Jabref)

Mandatory checks

• 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.

[github-actions]

The build for this PR is no longer available. Please visit https://builds.jabref.org/main/ for the latest build.

[Siedlerchr]

Let's first integrate this PR as it may produce conflicts otherwise
#10340 when the user reports back
My test was fine so far