Remove magic-nix-cache action which is deprecated

Author: malob

.github/workflows/ci.yml

@@ -42,9 +42,6 @@ jobs:
       - name: Install Nix
         uses: DeterminateSystems/nix-installer-action@v10
 
-      - name: Setup cache
-        uses: DeterminateSystems/magic-nix-cache-action@main
-
       - name: Build and test
         run: |
           NAME=$(nix eval --impure --raw --expr '(import ./constants.nix).name')-${{ matrix.ghc }}
@@ -62,9 +59,6 @@ jobs:
       - name: Install Nix
         uses: DeterminateSystems/nix-installer-action@v10
 
-      - name: Setup cache
-        uses: DeterminateSystems/magic-nix-cache-action@main
-
       - name: Build and test
         run: |
           nix -L develop . --command echo "OK"