Simplify action to use git from environment.

action.yml

@@ -1,34 +1,26 @@
 name: 'Initialize CI Environment and Repository for Flake Builds'
-description: 'Initialize a CI environment with nix (and also checkout the repository recursively with LFS)'
+description: |
+  Initialize a Nix Flakes CI environment (optionally with LFS).
 inputs:
   token:
     description: 'OAUTH token to access repositories'
     required: false
     default: ${{ github.token }}
   lfs:
-    description: Whether to enable lfs. Note that nix flakes don't support LFS currently.
+    description: Whether to enable lfs. Note that nix flake builds don't support LFS currently.
     required: false
-    default: true
+    default: false
 runs:
   using: "composite"
   steps:
-    - name: Setup NIX CI Environment
-      run: |
-        mkdir -p ~/.config/nix
-        echo "substituters = https://nixpkgs-cache.qo.is?priority=39" >> ~/.config/nix/nix.conf
-        echo "trusted-public-keys = cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=" >> ~/.config/nix/nix.conf
-        nix profile install nixpkgs#git-lfs nixpkgs#gnused
-
     - name: Checkout Repository
-      shell: "nix shell nixpkgs#git-lfs nixpkgs#gnused --command {0}"
+      shell: bash
       run: |
         if [ "${{ inputs.lfs }}" == "true" ]; then git lfs install; fi
-        GIT_SERVER=`echo -n "$GITHUB_SERVER_URL" | sed "s%https://%%"`
-        echo -e "machine $GIT_SERVER\nlogin oauth2\npassword ${{ inputs.token }}" > ~/.netrc
+        echo -e "machine ${GITHUB_SERVER_URL##https://}\nlogin oauth2\npassword ${{ inputs.token }}" > ~/.netrc
         # Disable clone protection to pull LFS as well
         GIT_CLONE_PROTECTION_ACTIVE=false git clone --branch $GITHUB_REF_NAME --recurse-submodules $GITHUB_SERVER_URL/$GITHUB_REPOSITORY .
         git submodule update --init --recursive
 
     - name: Prefetch git submodules in nix store
-      shell: "nix shell nixpkgs#nixVersions.nix_2_26 nixpkgs#git-lfs --command {0}"
       run: git submodule foreach --recursive 'nix flake prefetch'