Free up space before flake check

.github/workflows/validation.yml

@@ -8,6 +8,24 @@ jobs:
   keys:
     runs-on: ubuntu-latest
     steps:
+      - name: Maximize build space
+        uses: AdityaGarg8/remove-unwanted-software@v4.1
+        with:
+          verbose: 'true'
+          remove-dotnet: 'true'
+          remove-android: 'true'
+          remove-haskell: 'true'
+          remove-codeql: 'true'
+          remove-docker-images: 'true'
+          remove-large-packages: 'true'
+          remove-cached-tools: 'true'
+          remove-swapfile: 'true'
+      # Derivations are built under /tmp
+      - name: Bind mount /tmp
+        run: |
+          sudo mkdir /mnt/nix /nix
+          sudo chmod 0755 /nix
+          sudo mount --bind /mnt/nix /nix
       - name: Install dependencies
         run: |
           sudo apt-get update