[ci] Enable veccore on march=native build

We have no test coverage on Linux for these options right now.

We don't want to necessarily enable them in the release at this point,
but enabling them on the `march=native` build is the perfect opportunity
to test the VecCore features, in particular with the `std::simd`
backend.

Author: guitargeek

.github/workflows/root-ci.yml

@@ -402,7 +402,7 @@ jobs:
           - image: alma9
             is_special: true
             property: march_native
-            overrides: ["CMAKE_BUILD_TYPE=RelWithDebInfo", "CMAKE_CXX_FLAGS=-march=native", "CMAKE_C_FLAGS=-march=native", "builtin_zlib=ON", "builtin_zstd=ON"]
+            overrides: ["CMAKE_BUILD_TYPE=RelWithDebInfo", "CMAKE_CXX_FLAGS=-march=native", "CMAKE_C_FLAGS=-march=native", "builtin_zlib=ON", "builtin_zstd=ON", "builtin_veccore=ON", "veccore=ON"]
           - image: alma10
             is_special: true
             property: arm64