Merge pull request #479 from dropbox/jfein/gradle8-support

Switch to using property for gradle 8 support

dropbox-sdk-java/build.gradle

@@ -215,18 +215,17 @@ jar {
 }
 
 task jarWithoutOsgi(type: Jar, dependsOn: classes) {
-    classifier 'withoutOsgi'
+    archiveClassifier.set('withoutOsgi')
     from sourceSets.main.output
 }
 
 task sourcesJar(type: Jar, dependsOn: classes) {
-    classifier = 'sources'
+    archiveClassifier.set('sources')
     from sourceSets.main.allSource
 }
 
-
 task javadocJar(type: Jar, dependsOn: javadoc) {
-    classifier = 'javadoc'
+    archiveClassifier.set('javadoc')
     from javadoc.destinationDir
 }