UnknownSdkType - disallow creation by user

GitOrigin-RevId: cc9813e5b805b5e9d61e43c882ad5f2e6e6d453a

platform/lang-api/src/com/intellij/openapi/projectRoots/impl/UnknownSdkType.java

@@ -83,4 +83,9 @@ public class UnknownSdkType extends SdkType{
   public Icon getIcon() {
     return AllIcons.Nodes.UnknownJdk;
   }
+
+  @Override
+  public boolean allowCreationByUser() {
+    return false;
+  }
 }