fix(youtube-player): YT.Player is not a constructor

[Ronll]

fixes a race condition where window.YT would exist but window.YT.Player would not.

Fixes #20598

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[Ronll]

@googlebot I signed it!

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[crisbeto]

Can this be captured in a unit test? Otherwise we may end up regressing in the future.

[Ronll]

I modified the 'it waits until the api is ready before initializing' test to account for this case.

[crisbeto]

LGTM

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