Make nix build optional.

Signed-off-by: KtorZ <5680256+KtorZ@users.noreply.github.com>

.github/workflows/nix.yml

@@ -6,7 +6,6 @@ on:
 jobs:
   nix-build:
     runs-on: ubuntu-latest
-
     steps:
       - name: Checkout repository
         uses: actions/checkout@v3
@@ -20,5 +19,14 @@ jobs:
         uses: DeterminateSystems/magic-nix-cache-action@v1
 
       - name: Build Aiken
-        run: nix build
-
+        shell: bash
+        run: |
+          set +e
+          nix build
+          exitcode="$?"
+          if [[ "$exitcode" != "0" ]] ; then
+            echo "::warning::Nix build failed with exit code $exitcode"
+            exit 0
+          else
+            exit "$exitcode"
+          fi