extra_deps_from_github.txt is now only searched for in filesystem path only… so COPY over there

[SamuelMarks]

Description

FIXES: bug introduced in #2587

Tests

CI and on a TPU VM:

bash ./dependencies/scripts/docker_build_dependency_image.sh DEVICE=tpu MODE=stable

bash ./dependencies/scripts/docker_build_dependency_image.sh DEVICE=tpu MODE=nightly

Checklist

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• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.