wip: use runner.os variable

.forgejo/workflows/check.yml

@@ -27,15 +27,15 @@ jobs:
         uses: https://github.com/nix-community/cache-nix-action@v4
         id: nix-store-cache
         with:
-          key: cache-x86_64-linux-nix-store-${{ steps.flake-lock-hash.outputs.hash }}
+          key: cache-${{ runner.os }}-nix-store-${{ steps.flake-lock-hash.outputs.hash }}
           restore-keys: |
-            cache-x86_64-linux-nix-store-
+            cache-${{ runner.os }}-nix-store-
 
           gc-linux: true
           gc-max-store-size-linux: 10000000000
 
           purge-caches: true
-          purge-key: cache-x86_64-linux-nix-store-
+          purge-key: cache-${{ runner.os }}-nix-store-
           purge-created: true
           purge-created-max-age: 42
       - name: echo if no cache hit