Add a plain x86_64 slice to the dyld fixture while retaining both same-named arm64e slices and their independent environment assertions.
The original fixture was rejected by real x64 CLI admission before tracing. The contributing PR's complete Linux CI run passes all 30 jobs, including the portable suite. Codex and Greptile reviews completed without findings; no unresolved threads remain.
This restores the main test baseline needed for #2635. The change is limited to test data and preserves the original author's contribution.
Co-authored-by: Kaoru0822 <208281322+kaoru0822-kitauji@users.noreply.github.com>
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