Bump cachix/install-nix-action from 18 to 20 (#681)

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 18 to 20.
<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>install-nix-action-v20</h2>
<p><a href="https://discourse.nixos.org/t/nix-2-14-0-released/25900/4Fix">https://discourse.nixos.org/t/nix-2-14-0-released/25900/4Fix</a> support for Nix 2.14 new profile location: <a href="https://redirect.github.com/NixOS/nix/pull/5226">NixOS/nix#5226</a></p>
<h2>install-nix-action-v19</h2>
<ul>
<li>expose github_access_token option and use the default github token by default to prevent rate limiting</li>
<li>support <code>--no-daemon</code> installation</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/cachix/install-nix-action/commit/29bd9290ef037a3ecbdafe83cbd2185e9dd0fa0a"><code>29bd929</code></a> Merge pull request <a href="https://redirect.github.com/cachix/install-nix-action/issues/163">#163</a> from cachix/fix-nix-2.14</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/167742cb88c69ac5973aeb26d4ccced45567405e"><code>167742c</code></a> don't insist $USER needs to be set</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/3755e30bd2ebf4bf382dc45c20cffaacfb86a578"><code>3755e30</code></a> Support new Nix 2.14 profile PATH</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/193b0d85f5ef283d61e38ad64ceb5808dffb97b0"><code>193b0d8</code></a> Merge pull request <a href="https://redirect.github.com/cachix/install-nix-action/issues/159">#159</a> from cachix/update-readme</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/cb6121cc547d5925a2eca0fd04f753b21150f603"><code>cb6121c</code></a> Update README for v19</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/5c11eae19dba042788936d4f1c9685fdd814ac49"><code>5c11eae</code></a> Merge pull request <a href="https://redirect.github.com/cachix/install-nix-action/issues/158">#158</a> from cachix/fix-test</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/846213dc1f13fb2f1812c8be1d854b79948bde5a"><code>846213d</code></a> update tests</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/bd6084e16e55fded4460410222ed3c1a7fcd36c1"><code>bd6084e</code></a> Merge pull request <a href="https://redirect.github.com/cachix/install-nix-action/issues/156">#156</a> from InternetUnexplorer/update-readme</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/67388ca69eb5c94b15ffe79e08548ff5313663ef"><code>67388ca</code></a> Merge pull request <a href="https://redirect.github.com/cachix/install-nix-action/issues/157">#157</a> from zimbatm/default-token</li>
<li><a href="https://github.com/cachix/install-nix-action/commit/a4b8aaf5a24260b643f571235829e53e6b3cc920"><code>a4b8aaf</code></a> Fix rate-limits by using github.token by default</li>
<li>Additional commits viewable in <a href="https://github.com/cachix/install-nix-action/compare/v18...v20">compare view</a></li>
</ul>
</details>
<br />


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</details>

.github/workflows/ci.yaml

@@ -28,7 +28,7 @@ jobs:
         with:
           go-version: "${{ env.GO_VERSION }}"
       - name: Install nix
-        uses: cachix/install-nix-action@v18
+        uses: cachix/install-nix-action@v20
         with:
           nix_path: nixpkgs=channel:nixos-unstable
       - name: Install required nix packages
@@ -42,7 +42,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Install nix
-        uses: cachix/install-nix-action@v18
+        uses: cachix/install-nix-action@v20
         with:
           nix_path: nixpkgs=channel:nixos-unstable
       - run: nix-shell --run 'true'