fix(python): build GNU/Linux wheels with manylinux_2_28

[szmcdull]

Summary

• GNU/Linux Python wheels from the current build-python-sdk job are tagged manylinux_2_39 because they are built on the ubuntu-24.04 host without a manylinux container.
• Those wheels require glibc ≥ 2.39, so pip cannot install them on Ubuntu 22.04 (glibc 2.35). PyPI longbridge==4.5.0 already shows this (manylinux_2_39 / manylinux_2_39_aarch64).
• This change builds Ubuntu GNU/Linux wheels in a manylinux_2_28 container (glibc 2.28), which remains installable on Ubuntu 20.04, 22.04, and 24.04. Windows and macOS keep manylinux: off. The interpreter flag is aligned with the existing musl job (-i python${{ matrix.python-version }}).

Test plan

• Confirm GitHub Actions Release / build-python-sdk GNU/Linux artifacts are tagged manylinux_2_28 (x86_64 and aarch64), not manylinux_2_39.
• Confirm Windows and macOS wheel tags are unchanged.
• Install a built GNU/Linux wheel on Ubuntu 22.04 (pip install longbridge --no-index --find-links dist) and import longbridge.
• After the next SDK release, confirm PyPI GNU/Linux files are manylinux_2_28 and installable on Ubuntu 22.04.