osgi plugin has been removed from Gradle core plugins since Gradle 6, yet some builds still depend on it.
This repo extracts the legacy osgi plugin (and unit test) from Gradle 5.6.4 source code.
If you're still using the deprecated osgi Gradle plugin in Gradle 6+, you can use this plugin (com.github.blindpirate.osgi) as an option.
Just replace the original apply plugin: 'osgi' with apply plugin: 'com.github.blindpirate.osgi' or apply it in plugins block:
plugins {
id("com.github.blindpirate.osgi") version "0.0.7"
}