Gradle: Update the namespace check for plugins

It seems that the Kotlin DSL behavior has changed at some point and core
plugins now report "org.gradle" instead of null as their namespace.

Signed-off-by: Sebastian Schuberth <sschuberth@gmail.com>

settings.gradle.kts

@@ -2,7 +2,7 @@ pluginManagement {
     resolutionStrategy {
         eachPlugin {
             // Work around https://github.com/gradle/gradle/issues/1697.
-            if (requested.id.namespace != null && requested.version == null) {
+            if (requested.id.namespace != "org.gradle" && requested.version == null) {
                 val versionPropertyName = if (requested.id.id == "org.jetbrains.kotlin.jvm") {
                     "kotlinPluginVersion"
                 } else {