chore(deps): update cachix/install-nix-action action to v25 (#109)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
|
[cachix/install-nix-action](https://togithub.com/cachix/install-nix-action)
| action | major | `v24` -> `v25` |

---

### Release Notes

<details>
<summary>cachix/install-nix-action (cachix/install-nix-action)</summary>

###
[`v25`](https://togithub.com/cachix/install-nix-action/releases/tag/v25):
install-nix-action-v25

[Compare
Source](https://togithub.com/cachix/install-nix-action/compare/v24...v25)

Nix 2.19.2

</details>

---

### Configuration

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any time (no schedule defined).

🚦 **Automerge**: Enabled.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the
rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
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---

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[here](https://developer.mend.io/github/bobvanderlinden/nixpkgs-ruby).

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Author: renovate[bot]

.github/workflows/check.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Install Nix
-        uses: cachix/install-nix-action@v24
+        uses: cachix/install-nix-action@v25
       - uses: cachix/cachix-action@v13
         with:
           name: nixpkgs-ruby

.github/workflows/update.yml

@@ -16,7 +16,7 @@ jobs:
       with:
           ref: master
     - name: Install Nix
-      uses: cachix/install-nix-action@v24
+      uses: cachix/install-nix-action@v25
     - run: nix run .#update
       env:
         GITHUB_TOKEN: ${{secrets.GITHUB_TOKEN}}