build(deps): Bump cachix/install-nix-action from 20 to 21

[dependabot[bot]]

Bumps cachix/install-nix-action from 20 to 21.

Release notes

Sourced from cachix/install-nix-action's releases.

install-nix-action-v21

• pin Nix to 2.15.1 (recent releases broke too many things)
• fix the action to work on custom containers

Commits

• 4b933aa Nix: 2.15.1
• 3580693 Merge pull request #179 from joergdw/fix-action-path
• 3eb7a24 Merge pull request #178 from cachix/docs/149
• 840ed7c Document how to pass env vars to modern nix commands
• b2f4229 Fix action to make it work on custom containers;
• e304541 fix #170
• 3988b72 pin Nix to 2.15.0
• 763a380 Bump revision in README
• 67e9fd7 bump revision in readme
• be4cef7 Merge pull request #166 from l0b0/refactor/linting
• Additional commits viewable in compare view

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[what-the-diff[bot]]

PR Summary

• Updated cachix/install-nix-action version The version of the cachix/install-nix-action was upgraded from v20 to v21, ensuring the latest features and improvements are utilized.

[github-actions[bot]]

Since this pull request has not had any activity within the last 5 days, I have marked it as stale. I will close it if no further activity occurs within the next 5 days.

[dependabot[bot]]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version. You can also ignore all major, minor, or patch releases for a dependency by adding an ignore condition with the desired update_types to your config file.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.