ci: Remove the nix check from the CI run

Nobody is fixing it, so remove it. And if it should come back, make it
a dedicated workflow running on a nightly timer, not on the critical
path for PRs.

Author: cdecker

.github/workflows/ci.yaml

@@ -676,26 +676,6 @@ jobs:
           env
           cat config.vars
           VALGRIND=0 uv run eatmydata pytest tests/ -vvv ${GLOBAL_PYTEST_OPTS} -n ${PYTEST_PAR} ${PYTEST_OPTS}
-
-  check-flake:
-    name: Check Nix Flake
-    runs-on: ubuntu-22.04
-    strategy:
-      fail-fast: true
-    steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-        with:
-          submodules: 'recursive'
-      - name: Check Nix flake inputs
-        uses: DeterminateSystems/flake-checker-action@v8
-      - name: Install Nix
-        uses: cachix/install-nix-action@v31
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
-      - name: Check flake
-        run: nix flake check
-
   gather:
     # A dummy task that depends on the full matrix of tests, and
     # signals successful completion. Used for the PR status to pass