.github: bump install-nix-action (#631)

The new release addresses the issue with Nix 2.14.

https://github.com/cachix/install-nix-action/releases/tag/v20

.github/actions/common-setup/action.yml

@@ -11,9 +11,8 @@ runs:
   steps:
 
     - name: Installing Nix
-      uses: cachix/install-nix-action@v18
+      uses: cachix/install-nix-action@v20
       with:
-        install_url: https://releases.nixos.org/nix/nix-2.13.3/install
         nix_path: nixpkgs=channel:nixpkgs-unstable
         extra_nix_config: |
           access-tokens = github.com=${{ inputs.GITHUB_TOKEN }}

.github/workflows/update-flake-lock.yml

@@ -11,9 +11,8 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v3
       - name: Install Nix
-        uses: cachix/install-nix-action@v19
+        uses: cachix/install-nix-action@v20
         with:
-          install_url: https://releases.nixos.org/nix/nix-2.13.3/install
           extra_nix_config: |
             access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
       - name: Update flake.lock