Page Animations not inverted when navigating back

[flodaniel]

Describe the bug
When using the provided example to implement custom page transitions: #29 the animation for "forward" and "backward" navigation remains the same.
This only happens when handling the back navigation with the FlowBuilder state (context.flow().update...), but the animation behaves correctly if I use Navigator.pop(context);

This is a snipped of my onGeneratePages, where I tested the back navigation from OnboardingFlowPage.commuteDays to OnboardingFlowPage.enterAddress by calling context.flow<OnboardingState>.update((state) => OnboardingInitial(page: OnboardingFlowPage.enterAddress).

case OnboardingFlowPage.enterAddress:
      return [
        CustomPage.createWithoutAnalytics(
            EnterAddressFlow(isOnboarding: isOnboarding))
      ];
    case OnboardingFlowPage.commuteDays:
      return [
        CustomPage.createWithoutAnalytics(
            EnterAddressFlow(isOnboarding: isOnboarding)),
        CustomPage.createWithAnalytics(
            CommuteDaysPage(isOnboarding: isOnboarding)),
      ];

To Reproduce
Steps to reproduce the behavior:
Implement the given example with a custom page transition and do a back navigation by calling context.flow().update().

Expected behavior
A clear and concise description of what you expected to happen.
Inverted animation plays

Screenshots
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