ci(lspec): usingnix as package manager to handle lean4 and lake versions

Author: BRonen

.github/workflows/lspec.yml

@@ -9,12 +9,13 @@ jobs:
     name: Build
     runs-on: ubuntu-latest
     steps:
-      - name: install elan
-        run: |
-          set -o pipefail
-          curl -sSfL https://github.com/leanprover/elan/releases/download/v4.0.0/elan-x86_64-unknown-linux-gnu.tar.gz | tar xz
-          ./elan-init -y --default-toolchain none
-          echo "$HOME/.elan/bin" >> $GITHUB_PATH
       - uses: actions/checkout@v2
+      - uses: cachix/install-nix-action@v22
+        with:
+          nix_path: nixpkgs=channel:nixos-24.11
+      - name: Install Lean
+        run: nix-shell
+      - name: Log versions
+        run: lean --version && lake --version
       - name: run LSpec binary
         run: lake exe lspec