Try with caching?

.forgejo/workflows/nix.yaml

@@ -1,12 +1,24 @@
 on: [push]
 jobs:
-  test:
+  check:
     runs-on: nix
     steps:
     - name: Checkout
       uses: actions/checkout@v3
+        
+    - name: Restore cached nix store
+      id: cache-nix-store
+      uses: actions/cache/restore@v4
+      with:
+        path: /nix/store
+        key: ${{ runner.os }}-nix-store
+
     - name: Check
       run: |
-          pwd
-          ls -la .
         nix flake check
+
+    - name: Save nix store
+      uses: actions/cache/save@v4
+      with:
+        path: /nix/store
+        key: ${{ steps.cache-nix-store.outputs.cache-primary-key }}