Merge dependabot updates

Merge remote-tracking branches
'origin/dependabot/github_actions/cachix/cachix-action-16' and
'origin/dependabot/github_actions/cachix/install-nix-action-31'

Author: dehnert

.github/workflows/build.yml

@@ -47,7 +47,7 @@ jobs:
     - name: Checkout repository
       uses: actions/checkout@v4
     - name: Install nix
-      uses: cachix/install-nix-action@v30
+      uses: cachix/install-nix-action@v31
       with:
         nix_path: "${{ env.nixPath }}"
         extra_nix_config: |

.github/workflows/test.yml

@@ -19,7 +19,7 @@ jobs:
     - name: Checkout repository
       uses: actions/checkout@v4
     - name: Install nix
-      uses: cachix/install-nix-action@v30
+      uses: cachix/install-nix-action@v31
       with:
         nix_path: "${{ env.nixPath }}"
         extra_nix_config: |