Merge pull request #24966 from storybookjs/tom/fix-double-action

Test: Don't attach action to function mock if action was added already

code/addons/actions/src/loaders.ts

@@ -16,7 +16,7 @@ const attachActionsToFunctionMocks: LoaderFunction = (context) => {
     )
     .forEach(([key, value]) => {
       const previous = value.getMockImplementation();
-      if (previous?._actionAttached !== true) {
+      if (previous?._actionAttached !== true && previous?.isAction !== true) {
         const implementation = (...params: unknown[]) => {
           action(key)(...params);
           return previous?.(...params);