Drop python 3.8 in the CI

[vfdev-5]

Description:

• Drop python 3.8 in the CI
• EOL of python 3.8 is 2024-10, https://devguide.python.org/versions/

FIXED:
Problem with Horovod CPU CI for py3.10 and py3.11

 ignite/distributed/comp_models/horovod.py:159: in _HorovodDistModel
    "SUM": hvd.mpi_ops.Sum,
E   AttributeError: module 'horovod.torch' has no attribute 'mpi_ops'
Extension horovod.torch has not been built: /opt/hostedtoolcache/Python/3.10.15/x64/lib/python3.10/site-packages/horovod/torch/mpi_lib_v2.cpython-310-x86_64-linux-gnu.so not found
If this is not expected, reinstall Horovod with HOROVOD_WITH_PYTORCH=1 to debug the build error.
Warning! MPI libs are missing, but python applications are still available.