generic: Enable viaduct example test in CI

Signed-off-by: gatecat <gatecat@ds0.me>

.github/ci/build_generic.sh

@@ -20,6 +20,6 @@ function run_tests {
 function run_archcheck {
     pushd build
     # TODO
-    # ./nextpnr-generic --uarch example --test
+    ./nextpnr-generic --uarch example --test
     popd
 }