Bump cachix/install-nix-action from 30 to 31

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 30 to 31.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](https://github.com/cachix/install-nix-action/compare/v30...v31)

---
updated-dependencies:
- dependency-name: cachix/install-nix-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build-sd-image.yml

@@ -14,7 +14,7 @@ jobs:
         run: sudo apt-get install qemu-user-static
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         with:
           extra_nix_config: |
             system = aarch64-linux

.github/workflows/nix.yml

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       # TODO: add a binary cache
       # - uses: cachix/cachix-action@v10
       #   with:
@@ -33,5 +33,5 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v4
-      - uses: cachix/install-nix-action@v30
+      - uses: cachix/install-nix-action@v31
       - run: nix shell nixpkgs#alejandra -c alejandra -c .

.github/workflows/test-my-packages.yml

@@ -26,7 +26,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Install Nix
-        uses: cachix/install-nix-action@v30
+        uses: cachix/install-nix-action@v31
         # with:
         #   extra_nix_config: |
         #     # system = ${{ matrix.platform }}