flake.lock: Update (#203)

Automated changes by the
[update-flake-lock](https://github.com/DeterminateSystems/update-flake-lock)
GitHub Action.

```
Flake lock file updates:

• Updated input 'sops-nix':
    'github:Mic92/sops-nix/291aad29b59ceda517a06e59809f35cb0bb17c6b' (2024-03-04)
  → 'github:Mic92/sops-nix/25dd60fdd08fcacee2567a26ba6b91fe098941dc' (2024-03-06)
```

### Running GitHub Actions on this PR

GitHub Actions will not run workflows on pull requests which are opened
by a GitHub Action.

To run GitHub Actions workflows on this PR, run:

```sh
git branch -D update_flake_lock_action
git fetch origin
git checkout update_flake_lock_action
git commit --amend --no-edit
git push origin update_flake_lock_action --force
```

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