[Label Issue]: Add raw.githubusercontent.com to the whitelist for Validation-Domain.

Nobody has claimed this yet.

Disclaimer 1 before the following paragraphs: I admit and acknowledge I'm getting burnt out fast over the course of the past few days, so if I seem rough in some way, I apologise in advance.

Disclaimer 2: I learnt earlier today that `raw.github.com` was still an operational domain. I had previously thought GitHub had shut down that subdomain many years ago, but it at least seems to be a working substitute.

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So, `github.com` is this repo's gold standard for InstallerUrl-s. `raw.githubusercontent.com` is the default file host domain of `github.com`.

Despite that, `raw.githubusercontent.com` throws *"One or more of the installer URLs doesn't appear valid."* and the `Validation-Domain` label when used.

Surely it would be a clearcut case to get it globally whitelisted in this repo.

It would've made my discovery today of a GitHub InstallerUrl for the following a sunshine story that would've brightened me up:
* #378945.

Instead I stood completely flabbergasted and astounded at the time the pipeline results ticked in (https://github.com/microsoft/winget-pkgs/pull/378945#issuecomment-4679710722).

Review the Validation-Domain validation and the installer URL discussed in #378945 first. Trace where the pipeline rejects raw.githubusercontent.com, then verify that adding the domain to the whitelist makes the referenced installer URL pass validation without weakening other URL checks.

Written by the indexing model from the issue text.