Revert "Remove block_until_head_timeout_eager_prefetch test override"

This reverts commit 03716983faf5d10624e0af646dc2e7503cdb18b7.

Reason for revert: Suspected to cause fails on ci.chromium.org/ui/p/chromium/builders/ci/Linux%20Tests%20%28dbg%29%281%29

Bug: 356622798
Original change's description:
> Remove block_until_head_timeout_eager_prefetch test override
>
> Web platform tests should, in general, run under the same configuration
> we ship to our users, or at least the same as experimental web platform
> features. This is the first step in removing some of the overrides we
> are currently using.
>
> This required updating two web platform tests which were written to
> assume an infinite block-until-head timeout, and thus did not pass on
> stable Chromium as shipped to users and shown on https://wpt.fyi/.
>
> Eventually, it might be good to remove these block_until_head_timeout
> parameters, at least for speculation rules.
>
> Bug: 356622798
> Change-Id: If4b00cfbfbe5d6c7cf2dd55a3428a129e40868f6
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6636809
> Reviewed-by: Kent Tamura <tkent@chromium.org>
> Reviewed-by: Hiroshige Hayashizaki <hiroshige@chromium.org>
> Commit-Queue: Domenic Denicola <domenic@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1474799}

Bug: 356622798
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I50ee9efb9f2b9972dd43cfa282b46317dd275d4a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6650667
Owners-Override: Alexandra Reimers <areimers@chromium.org>
Auto-Submit: Alexandra Reimers <areimers@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Alexandra Reimers <areimers@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1474891}