Disable Cachix pushes

[danieldk]

What does this PR do?

This is not safe until we have sandboxed builds. For TGI alone this might not be a huge issue, but with Cachix caching disabled in hf-nix, TGI CI would build all the packages and push it to our cache.

Fixes # (issue)

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
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• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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[drbh]

LGTM

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[drbh]

merging as these changes only contain a small CI change and the failing CI was introduced in prior changes

• auto doc first seen: https://github.com/huggingface/text-generation-inference/actions/runs/16727413990/job/47346654379
• nix test formatting issue first seen: https://github.com/huggingface/text-generation-inference/actions/runs/16727413996/job/47346654554