chore(deps): update cachix/install-nix-action action to v31

Author: renovate[bot]

.github/workflows/test.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       - uses: cachix/cachix-action@v16
         with:
           name: devenv
@@ -25,7 +25,7 @@ jobs:
       - tests
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       - uses: cachix/cachix-action@v16
         with:
           name: devenv