attribute desugar_jdk_libs, which the licence collector cannot see

desugar_jdk_libs is bundled by core library desugaring rather than the
runtime classpath, so it never reached the generated licence list. Add it
plus its GPL-2.0-with-Classpath-Exception text via the plugin's manual
config directory.

app/build.gradle.kts

@@ -76,6 +76,12 @@ ksp {
     arg("room.schemaLocation", "$projectDir/schemas")
 }
 
+aboutLibraries {
+    collect {
+        configPath = file("config")
+    }
+}
+
 val integrationTestClasses =
     listOf(
         "com.subtracks.data.source.subsonic.SubsonicSourceIntegrationTest",