[Nix] Update cachix/install-nix-action version to v31

[hugtalbot]

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I have read, understand, and agree SOFA Developer Certificate of Origin (DCO).

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).

[github-actions]

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@hugtalbot your PR title is not following the required format ✏️
- PR title should provide a prefix scope, e.g. [MechanicalLoad]
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