Use native nix actions in CI

.github/workflows/ci.yaml

@@ -40,39 +40,8 @@ jobs:
         with:
           fetch-depth: 2
 
-      # The runner comes with all this software pre-installed: https://github.com/actions/virtual-environments/blob/main/images/linux/Ubuntu2004-README.md
-      # so we delete some large packages to make sure we have more space available.
-      #
-      # We print the remaining disk space between commands in order to have an idea of which of them
-      # have the most significant impact.
-      #
-      # Copied from https://github.com/jens-maus/RaspberryMatic/blob/ea6b8ce0dd2d53ea88b2766ba8d7f8e1d667281f/.github/workflows/ci.yml#L34-L40
-      # and https://github.com/actions/virtual-environments/issues/709#issuecomment-612569242
-      - name: Free disk space
-        run: |
-          df --human-readable
-          sudo apt-get remove --yes '^dotnet-.*' '^llvm-.*' 'php.*' azure-cli google-cloud-sdk hhvm google-chrome-stable firefox powershell
-          df --human-readable
-          sudo apt-get autoremove --yes
-          df --human-readable
-          sudo apt clean
-          df --human-readable
-          docker rmi $(docker image ls --all --quiet)
-          df --human-readable
-          rm --recursive --force "$AGENT_TOOLSDIRECTORY"
-          df --human-readable
-          rm --recursive --force /usr/local/share/boost
-          df --human-readable
-          sudo swapoff --all
-          df --human-readable
-          sudo rm --force /swapfile
-          df --human-readable
-
-      - name: Docker pull
-        timeout-minutes: 10
-        run: |
-          ./scripts/docker_pull
-          df --human-readable
+      - uses: DeterminateSystems/nix-installer-action@main
+      - uses: DeterminateSystems/magic-nix-cache-action@main
 
       - name: Run command
         env:
@@ -81,10 +50,9 @@ jobs:
           # Do not run tests that require KVM on GitHub Actions, since nested virtualization is not supported.
           OAK_KVM_TESTS: skip
         run: |
-          ./scripts/docker_run nix develop .#ci --command ./scripts/xtask --scope=all ${{ matrix.cmd }}
-          df --human-readable
+          nix develop .#ci --command ./scripts/xtask --scope=all ${{ matrix.cmd }}
 
         # Ensure that the previous steps did not modify our source-code and that
         # relevant build artifacts are ignored by git.
       - name: Git check diff
-        run: ./scripts/docker_run ./scripts/git_check_diff
+        run: ./scripts/git_check_diff