Amp-ima-video bug

### Description

it seems that the amp-video-ima component is not supporting video "overlays" I have tested this with the google sample tags on the demo page and can also re-produce it locally,

### Reproduction Steps

if you put this tag in the demo page it will not show an "overlay"https://pubads.g.doubleclick.net/gampad/ads?iu=/21775744923/external/nonlinear_ad_samples&sz=480x70&cust_params=sample_ct%3Dnonlinear&ciu_szs=300x250%2C728x90&gdfp_req=1&output=vast&unviewed_position_start=1&env=vp&impl=s&correlator=

in demo page:
https://playground.amp.dev/?url=https%3A%2F%2Fpreview.amp.dev%2Fdocumentation%2Fexamples%2Fcomponents%2Famp-ima-video&format=websites&_gl=1*x3blfa*_ga*YW1wLVh6RmlUWWlTOV91c0ZaV0QzUWZyQ0E.&mode=Responsive

### Relevant Logs

_No response_

### Browser(s) Affected

Chrome

### OS(s) Affected

_No response_

### Device(s) Affected

_No response_

### AMP Version Affected

_No response_

Start by reproducing the missing overlay in the amp-ima-video demo page using the provided Google sample tag, then inspect the amp-ima-video component implementation and its existing tests or entry points. Done means the sample nonlinear video overlay is displayed correctly in Chrome without regressing the component’s existing behavior.

Written by the indexing model from the issue text.