use root context store for caching config value

Co-authored-by: Marc Philipp <mail@marcphilipp.de>

junit-jupiter-params/src/main/java/org/junit/jupiter/params/ParameterizedTestExtension.java

@@ -116,7 +116,7 @@ private ExtensionContext.Store getStoreInMethodNamespace(ExtensionContext contex
 	}
 
 	private ExtensionContext.Store getStoreInExtensionNamespace(ExtensionContext context) {
-		return context.getStore(Namespace.create(ParameterizedTestExtension.class));
+		return context.getRoot().getStore(Namespace.create(ParameterizedTestExtension.class));
 	}
 
 	private void validateArgumentCount(ExtensionContext extensionContext, Arguments arguments) {