Make go_bazel_test pass with Bzlmod enabled

[fmeum]

This is a quick fix for the test runner only, the tests themselves still rely on WORKSPACE (via local_repository). The rules_go repo is also hardcoded, which means that other external repos likely won't work.

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[fmeum]

@tyler-french @linzhp This is the minimal change needed to get go_bazel_test to pass in the Gazelle repo.

The automatic collection of repos from runfiles is problematic with Bzlmod since we have no easy way of knowing the apparent name. If we decide to stick with it, I can probably make it work by generating and parsing repo_mapping files, but even that may not work due to the differences between local_repository and a proper Bazel module.

A better solution would be to rewrite the tests to use Bzlmod exclusively and, with the exception of the current repo, load all deps from the BCR instead of from runfiles. That's quite a non-trivial task though.