ci/tumbleweed: enable NDEBUG with gcc build

To increase build diversity.

.github/workflows/build.yml

@@ -297,6 +297,7 @@ jobs:
         config:
           - cc: "gcc"
             cxx: "g++"
+            args: "-Db_ndebug=true"
           - cc: "clang"
             cxx: "clang++"
             ld: "lld"