[mediaset] Update extractor

[aaron-tan]

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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

Mediaset underwent a name change. It used to be called mediasetplay but it's now called mediainfinity. Hence why downloads were failing. I've looked through previous pull requests and this isn't the first time it has undergone a name change so this is the latest update. It's basically the same site so I didn't change much in the extractor, only updated the regex to capture the new format of the URL.

• Updated the regex to reflect the name change.
• Changed the site URL of the first test to one that uses the new name change.

This should close #32491

[aaron-tan]

Thanks for the suggestion. I had not realised that static3.mediasetinfinity.mediaset.it did not exist

[audetto]

This PR does fix the mediasetinfinity download issue.