SWPROT-8953: build: ci: Allow build in forks .g/w/build-rootfs.yml

Signed-off-by: Philippe Coval <philippe.coval@silabs.com>

Author: rzr

.github/workflows/build-rootfs.yml

@@ -45,8 +45,10 @@ jobs:
           ./scripts/build-rootfs.sh docs/dist
       - name: Upload Release Asset
         id: upload-release-asset
+        env:
+          token-defined: ${{ secrets.GH_UNIFY_ACCESS_TOKEN != '' }}
+        if: ${{ env.token-defined == true && startsWith(github.ref, 'refs/tags/') }}
         uses: softprops/action-gh-release@v2
-        if: startsWith(github.ref, 'refs/tags/')
         with:
           files: build/dist/*
           # yamllint disable-line rule:line-length