build(deps): bump cachix/install-nix-action from 25 to 26 (#202)

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 25 to 26.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a href="https://github.com/cachix/install-nix-action/releases">cachix/install-nix-action's releases</a>.</em></p>
<blockquote>
<h2>v26</h2>
<p>Bump to Nix 2.20.5 to address CVE-2024-27297 / GHSA-2ffj-w4mj-pg37.</p>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/cachix/install-nix-action/commit/8887e596b4ee1134dae06b98d573bd674693f47c"><code>8887e59</code></a> Nix: 2.20.5</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/39a075cc21e415568870fbcfee53551b3764501d"><code>39a075c</code></a> bump</li>
<li>See full diff in <a href="https://github.com/cachix/install-nix-action/compare/v25...v26">compare view</a></li>
</ul>
</details>
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</details>

Author: mergify[bot]

.github/workflows/ci.yaml

@@ -35,7 +35,7 @@ jobs:
           echo ::set-output name=short::$(git rev-parse --short HEAD)
 
       - name: Install nix
-        uses: cachix/install-nix-action@v25
+        uses: cachix/install-nix-action@v26
         with:
           nix_path: nixpkgs=channel:nixos-unstable