[QA] Count doesn't change while swiping to another slide

### Description

Count doesn't change while swiping to another slide

### Reproduction Steps

Test Case - [Image Galleries with amp-carousel/Linking carousels]

Playground Link - https://playground.amp.dev/?url=https%3A%2F%2Fpreview.amp.dev%2Fdocumentation%2Fexamples%2Fmultimedia-animations%2Fimage_galleries_with_amp-carousel&format=websites&preview=true

Steps:
1) Launch playground link.
2) Scroll down to 4th image.
3) Swipe left to see the next image.

Observed : Slide count doesn't change.
http://recall/-/hs0wNzze8G3KGS0hZUyKJT/dm0jFoAOuXG5Ot8F6sTtLK

Expected : Slide count should change even with the swipe.

NOTE : Clicking on the next arrow on the image changes the count.

### Relevant Logs

_No response_

### Browser(s) Affected

Chrome, Firefox, Safari

### OS(s) Affected

NA

### Device(s) Affected

NA

### AMP Version Affected

2308112021001

Start by reproducing the issue in the linked AMP Playground example for image galleries with amp-carousel, comparing swipe navigation with the next-arrow behavior. Trace the amp-carousel handling of swipe events and slide-count updates; done means the count changes when swiping to another image in Chrome, Firefox, and Safari.

Written by the indexing model from the issue text.