$sf is not defined within the Google safeFrame when not checked in google admanager

### Description

all AMP creatives served through google `

Here's the setup on google admanager. If i checked the `serve into safeframe` option i have access to the sf api

I think when serving ads into safeframe, $sf api should be available by default

Thx for your help :)

### Reproduction Steps

Go on this page :
https://seedtagtest.com/2021/09/03/test-seedtag-false/amp/

open a JS console. and locate the safeframe window

try to call `window.$sf` in this scope and you'll get the exception `$sf` is not defined

### Relevant Logs

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### Browser(s) Affected

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### OS(s) Affected

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### Device(s) Affected

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### AMP Version Affected

_No response_