Make url for "client" referrer mandatory
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I added a url attribute to `Referrer::Client` so that the referrer header can be set accordingly when fetching.
`Referrer::Client` has to be kept separate from `Referrer::ReferrerUrl` as they differ in this method
6b0d9afd6f/components/script/dom/request.rs (L566-L576)
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- [X] These changes fix#26570 (GitHub issue number if applicable)
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