Update nix-dev-cache workflow

The previous version of cachix/install-nix-action installed too old of a
Nix version to allow sandboxing on macOS.

Author: sellout

.github/workflows/nix-dev-cache.yaml

@@ -33,15 +33,15 @@ jobs:
       run: |
         sudo mkdir /nix /mnt/nix
         sudo mount --bind /mnt/nix /nix
-    - uses: cachix/install-nix-action@ba0dd844c9180cbf77aa72a116d6fbc515d0e87b # v27
+    - uses: cachix/install-nix-action@9280e7aca88deada44c930f1e2c78e21c3ae3edd # v31.7
       if: runner.os == 'Linux'
       with:
         extra_nix_config: |
           extra-trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ=
           extra-substituters = https://cache.iog.io
     - uses: cachix/install-nix-action@ba0dd844c9180cbf77aa72a116d6fbc515d0e87b # v27
       if: runner.os != 'Linux'
-    - uses: cachix/cachix-action@ad2ddac53f961de1989924296a1f236fcfbaa4fc # v15
+    - uses: cachix/install-nix-action@9280e7aca88deada44c930f1e2c78e21c3ae3edd # v31.7
       with:
         name: unison
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'