Make GlobalRegistry accept generic types

Author: Kiber2009

src/main/java/io/github/kiber2009/plugin/contentapi/registry/GlobalRegistry.java

@@ -23,7 +23,7 @@ protected void registerItem(final @NonNull NamespacedKey key, final @NonNull T v
         map.put(key, value);
     }
 
-    public void register(final @NonNull LocalRegistry<T> registry) {
+    public void register(final @NonNull LocalRegistry<? extends T> registry) {
         for (final NamespacedKey key : registry.keySet())
             registerItem(key, Objects.requireNonNull(registry.get(key)));
     }