[jar] SecurityException: Invalid signature file digest for Manifest main attributes

When executing the .jar file (with the correct Java version, i.e., 15+), the following error appears. This comes from signatures of daughter .jar files we're shipping, if I understand it correctly, and can be solved by simply stripping those signatures. I already have a commit for this, MR incoming...

I don't think it's a problem to strip the signatures, as we already verify the dependencies integrity with gradle-witness. Once we publish "real" .jar files, we should sign them somehow, though.

➜  /tmp cd jdk-17.0.1 
➜  jdk-17.0.1 cd bin 
➜  bin ./java -jar /home/briar/Documents/briar-desktop/build/compose/jars/Briar-linux-x64-0.0.1.jar                                                            
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.SecurityException: Invalid signature file digest for Manifest main attributes
	at java.base/sun.security.util.SignatureFileVerifier.processImpl(SignatureFileVerifier.java:340)
	at java.base/sun.security.util.SignatureFileVerifier.process(SignatureFileVerifier.java:282)
	at java.base/java.util.jar.JarVerifier.processEntry(JarVerifier.java:277)
	at java.base/java.util.jar.JarVerifier.update(JarVerifier.java:234)
	at java.base/java.util.jar.JarFile.initializeVerifier(JarFile.java:762)
	at java.base/java.util.jar.JarFile.ensureInitialization(JarFile.java:1033)
	at java.base/java.util.jar.JavaUtilJarAccessImpl.ensureInitialization(JavaUtilJarAccessImpl.java:72)
	at java.base/jdk.internal.loader.URLClassPath$JarLoader$2.getManifest(URLClassPath.java:883)
	at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:848)
	at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760)
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
	at java.base/java.lang.Class.forName0(Native Method)
	at java.base/java.lang.Class.forName(Class.java:467)
	at java.base/sun.launcher.LauncherHelper.loadMainClass(LauncherHelper.java:780)