chore(deps): update determinatesystems/nix-installer-action action to v20 (#306)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
|
[DeterminateSystems/nix-installer-action](https://redirect.github.com/DeterminateSystems/nix-installer-action)
| action | major | `v19` -> `v20` |

---

### Release Notes

<details>
<summary>DeterminateSystems/nix-installer-action
(DeterminateSystems/nix-installer-action)</summary>

###
[`v20`](https://redirect.github.com/DeterminateSystems/nix-installer-action/releases/tag/v20)

[Compare
Source](https://redirect.github.com/DeterminateSystems/nix-installer-action/compare/v19...v20)

#### What's Changed

- Update `detsys-ts`: Merge pull request
[#&#8203;106](https://redirect.github.com/DeterminateSystems/nix-installer-action/issues/106)
from DeterminateSystems/fix-dependabot-warning by
[@&#8203;detsys-pr-bot](https://redirect.github.com/detsys-pr-bot) in
[#&#8203;194](https://redirect.github.com/DeterminateSystems/nix-installer-action/pull/194)
- Update `detsys-ts`: Capture the version of Nix in addition to the nix
store version
([#&#8203;108](https://redirect.github.com/DeterminateSystems/nix-installer-action/issues/108))
by [@&#8203;detsys-pr-bot](https://redirect.github.com/detsys-pr-bot) in
[#&#8203;197](https://redirect.github.com/DeterminateSystems/nix-installer-action/pull/197)
- Report the number of nix builds that passed / failed by
[@&#8203;grahamc](https://redirect.github.com/grahamc) in
[#&#8203;196](https://redirect.github.com/DeterminateSystems/nix-installer-action/pull/196)
- Record events if authentication is skipped by
[@&#8203;gustavderdrache](https://redirect.github.com/gustavderdrache)
in
[#&#8203;198](https://redirect.github.com/DeterminateSystems/nix-installer-action/pull/198)
- Treat FlakeHub logins as a funnel by
[@&#8203;gustavderdrache](https://redirect.github.com/gustavderdrache)
in
[#&#8203;199](https://redirect.github.com/DeterminateSystems/nix-installer-action/pull/199)
- Apply fixups from CodeRabbit review by
[@&#8203;gustavderdrache](https://redirect.github.com/gustavderdrache)
in
[#&#8203;200](https://redirect.github.com/DeterminateSystems/nix-installer-action/pull/200)

**Full Changelog**:
<DeterminateSystems/nix-installer-action@v19...v20>

</details>

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.github/actions/nix-setup/action.yaml

@@ -11,7 +11,7 @@ runs:
   using: composite
   steps:
     - name: Install Nix package manager
-      uses: DeterminateSystems/nix-installer-action@90bb610b90bf290cad97484ba341453bd1cbefea # v19
+      uses: DeterminateSystems/nix-installer-action@786fff0690178f1234e4e1fe9b536e94f5433196 # v20
       with:
         extra-conf: |
           experimental-features = nix-command flakes