[smart_holder] Fix terrible merge accident: `PYBIND11_INTERNALS_SH_DEF`...

[smart_holder] Fix terrible merge accident: `PYBIND11_INTERNALS_SH_DEF` missing in `PYBIND11_INTERNALS_ID` and `PYBIND11_MODULE_LOCAL_ID` (#5159)

* Fix oversight: Add `-DCMAKE_CXX_FLAGS="-DPYBIND11_USE_SMART_HOLDER_AS_DEFAULT"` for new `manylinux` job (Manylinux on 🐍 3.13t • GIL).

* Fix terrible merge accident introduced with pybind/pybind11#5085: `PYBIND11_INTERNALS_SH_DEF` was accidentally removed from `PYBIND11_INTERNALS_ID` and `PYBIND11_MODULE_LOCAL_ID`.