chore(deps): update cachix/cachix-action action to v15 (#73)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [cachix/cachix-action](https://togithub.com/cachix/cachix-action) |
action | major | `v14` -> `v15` |

---

### Release Notes

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

### [`v15`](https://togithub.com/cachix/cachix-action/releases/tag/v15):
cachix-action-v15

[Compare
Source](https://togithub.com/cachix/cachix-action/compare/v14...v15)

#### What's Changed

- Pass `cachixArgs` to the daemon by
[@&#8203;sandydoo](https://togithub.com/sandydoo) in
[https://github.com/cachix/cachix-action/pull/177](https://togithub.com/cachix/cachix-action/pull/177)
- Support path filtering when using the daemon by
[@&#8203;sandydoo](https://togithub.com/sandydoo) in
[https://github.com/cachix/cachix-action/pull/182](https://togithub.com/cachix/cachix-action/pull/182)
- Skip prep steps if using `pathsToPush` by
[@&#8203;sandydoo](https://togithub.com/sandydoo) in
[https://github.com/cachix/cachix-action/pull/180](https://togithub.com/cachix/cachix-action/pull/180)
- store-scan: improve error handling when listing the store fails by
[@&#8203;sandydoo](https://togithub.com/sandydoo) in
[https://github.com/cachix/cachix-action/pull/183](https://togithub.com/cachix/cachix-action/pull/183)

**Full Changelog**:
https://github.com/cachix/cachix-action/compare/v14...v15

</details>

---

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---

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---

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.github/workflows/nix.yml

@@ -39,7 +39,7 @@ jobs:
         with:
           extra_nix_config: |
             access-tokens = github.com=${{ github.token }}
-      - uses: cachix/cachix-action@v14
+      - uses: cachix/cachix-action@v15
         continue-on-error: true
         with:
           name: vault-auth-tee