wip: cachix actions needs USER env

.forgejo/workflows/check.yml

@@ -4,6 +4,8 @@ on: [push]
 jobs:
   Check:
     runs-on: ubuntu-latest
+    env:
+      USER: root
     steps:
       - name: Check out repository code
         uses: https://code.forgejo.org/actions/checkout@v4
@@ -11,8 +13,6 @@ jobs:
         run: "apt update && apt install -y sudo"
       - name: Install nix
         uses: https://github.com/cachix/install-nix-action@v23
-      - name: Set USER to make cachix happy
-        run: "export USER=root"
       - name: Prepare cachix
         uses: https://github.com/cachix/cachix-action@v12
         with: