[CI] Introduce a simple py38 ci for syntax compatibility

[LeiWang1999]

@XuehaiPan, I agree. However, we should maintain support for Python 3.8 due to some reasons. We plan to deprecate Python 3.8 in the future once we integrate with TVM-FFI. In the meantime, I suggest introducing a simple CI that imports tilelang and runs a quick gemm test to verify python 3.8 syntax support. @yyttt6, cc'ing you when you have time.

Originally posted by @LeiWang1999 in #959 (comment)

[LeiWang1999]

better solution proposed by #963 , closed.