maybe it it wonna work this way?

.github/workflows/nix-github-actions.yml

@@ -13,16 +13,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
 
-    - name: Free Disk Space (Ubuntu)
-      uses: jlumbroso/free-disk-space@main
-      with:
-        # this might remove tools that are actually needed,
-        # if set to "true" but frees about 6 GB
-        tool-cache: true
-
-        # all of these default to true, but feel free to set to
-        # "false" if necessary for your workflow
-        swap-storage: false
 
   nix-matrix:
     needs: free-disk-space
@@ -60,6 +50,15 @@ jobs:
     strategy:
       matrix: ${{fromJSON(needs.nix-matrix.outputs.matrix)}}
     steps:
+      - uses: jlumbroso/free-disk-space@main
+        with:
+        # this might remove tools that are actually needed,
+        # if set to "true" but frees about 6 GB
+          tool-cache: true
+
+        # all of these default to true, but feel free to set to
+        # "false" if necessary for your workflow
+          swap-storage: true
       - uses: actions/checkout@v4
       - uses: cachix/install-nix-action@v27
       - uses: cachix/cachix-action@v15