build: update dependency io_bazel_rules_webtesting to v0.4.0

[dgp1130]

Forked off #30465, as @rules_webtesting seems to have changed its URL format.

[dgp1130]

This seems to be causing a few breakages in the @devinfra workspace. We're planning to move to @rules_browsers anyways, so it seems easier to just ignore this update for now.

[angular-automatic-lock-bot]

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