CI: Upload fuzz crashers on failure

The step was skipped because the previous one failed. This should now
only upload on failures.

Signed-off-by: Patrick East <east.patrick@gmail.com>

.github/workflows/nightly.yaml

@@ -36,6 +36,7 @@ jobs:
         run: make ci-go-check-fuzz
 
       - name: Upload Workdir
+        if: ${{ failure() }}
         uses: actions/upload-artifact@v2
         with:
           name: workdir