Make sure $url is a string before calling str_contains(). (#35605)

* Make sure $url is a string before calling str_contains().

The jetpack_oembed_timeout_override() filter expects to always get a URL
as a string.  There are times where that is not the case, being given an
array instead.  Defend against that condition.

* Update changelog entry

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Co-authored-by: Jeremy Herve <jeremy@jeremy.hu>

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/7876938939