Bug 1844392 [wpt PR 41110] - [FedCM] Add tests for sec-fetch-{mode, site}, a=testonly

Bug 1844392 [wpt PR 41110] - [FedCM] Add tests for sec-fetch-{mode, site}, a=testonly

Automatic update from web-platform-tests
[FedCM] Add tests for sec-fetch-{mode, site}

In the process, I found out that we set an incorrect originator --
it should be an opaque origin per the spec:
https://fedidcg.github.io/FedCM/#fetch-config-file

This difference matters because the tests actually connect to the
IDP on the same host, which would lead to a sec-fetch-site value
of `same-site`, when we actually always want it to be `cross-site`.

R=npm@chromium.org

Change-Id: If6b4f45ec948ef251ceed50077043005d537cb66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4702024
Commit-Queue: Nicolás Peña <npm@chromium.org>
Reviewed-by: Nicolás Peña <npm@chromium.org>
Auto-Submit: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1172446}

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wpt-commits: d8cce53af1032350188ac4f15f0ba9294cd8f494
wpt-pr: 41110