test: fix mock for useStripe (#1559)

`useStripe` returns functions rather than other hooks.

In reality it doesn't return all functions from the `mockFunctions` object, but using a superset for the mock should still be fine as TS won't allow calling the functions which are not in the declared type of the hook.

jest/mock.js

@@ -186,5 +186,5 @@ module.exports = {
   GooglePayButton: () => 'GooglePayButton',
   AddToWalletButton: () => 'AddToWalletButton',
   PlatformPayButton: () => 'PlatformPayButton',
-  useStripe: jest.fn(() => mockHooks),
+  useStripe: jest.fn(() => mockFunctions),
 };