Try to use koppor/gradle-modules-plugin "release" (made in fork)

[koppor]

JitPack has issues. https://status.jitpack.io/

A problem occurred configuring root project 'JabRef'.
> Could not resolve all artifacts for configuration ':classpath'.
   > Could not resolve com.github.koppor.gradle-modules-plugin:gradle-modules-plugin:jitpack-SNAPSHOT.
     Required by:
         project : > com.github.koppor:gradle-modules-plugin:jitpack-SNAPSHOT:d68df40569-1
      > Could not resolve com.github.koppor.gradle-modules-plugin:gradle-modules-plugin:jitpack-SNAPSHOT.
         > Could not get resource 'https://jitpack.io/com/github/koppor/gradle-modules-plugin/gradle-modules-plugin/jitpack-SNAPSHOT/gradle-modules-plugin-jitpack-d68df40569-1.pom'.
            > Could not HEAD 'https://jitpack.io/com/github/koppor/gradle-modules-plugin/gradle-modules-plugin/jitpack-SNAPSHOT/gradle-modules-plugin-jitpack-d68df40569-1.pom'.
               > Read timed out
> There are 6 more failures with identical causes.

This should be "fixed" by pinning the plugin to a concrete version.

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]

We should get this fixed either in the original or submit your plugin to gradle repo or maven central. Jitpack is unreliable.