build(deps): bump cachix/install-nix-action from 18 to 20

Bumps [cachix/install-nix-action](https://github.com/cachix/install-nix-action) from 18 to 20.
- [Release notes](https://github.com/cachix/install-nix-action/releases)
- [Commits](https://github.com/cachix/install-nix-action/compare/v18...v20)

---
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/Cabal-Linux-Remote.yml

@@ -44,7 +44,7 @@ jobs:
 
       # Still required for Remote
       - name: "Install Nix"
-        uses: cachix/install-nix-action@v18
+        uses: cachix/install-nix-action@v20
         if: matrix.packageRoot == 'hnix-store-remote'
 
       # Remote: Enabling testsuite, because it requires networking in the default Nix environment.

.github/workflows/On-Release-Cabal-Linux.yml

@@ -43,7 +43,7 @@ jobs:
 
       # Still required for Remote
       - name: "Install Nix"
-        uses: cachix/install-nix-action@v18
+        uses: cachix/install-nix-action@v20
         if: matrix.packageRoot == 'hnix-store-remote'
 
       # Remote: Enabling testsuite, because it requires networking in the default Nix environment.

.github/workflows/Optional-Nix-dev-env-main.yml

@@ -32,7 +32,7 @@ jobs:
       with:
         submodules: recursive
     - name: "Install Nix"
-      uses: cachix/install-nix-action@v18
+      uses: cachix/install-nix-action@v20
       with:
         nix_path: nixpkgs=channel:nixos-unstable
     - name: "Install Cachix"