CI: build torch-mlir python package for Python v3.8 (llvm#1827)

Previously, torchvision had not released WHL files for Python v3.8,
causing failures in torch-mlir python package builds, so we had disabled
building for Python v3.8.

Now that the WHL files are back, this patch re-enables v3.8 builds.

build_tools/python_deploy/build_linux_packages.sh

@@ -44,7 +44,7 @@ TM_RELEASE_DOCKER_IMAGE="${TM_RELEASE_DOCKER_IMAGE:-stellaraccident/manylinux201
 # ./build_tools/docker/Dockerfile
 TM_CI_DOCKER_IMAGE="${TM_CI_DOCKER_IMAGE:-powderluv/torch-mlir-ci:latest}"
 # Version of Python to use in Release builds. Ignored in CIs.
-TM_PYTHON_VERSIONS="${TM_PYTHON_VERSIONS:-cp310-cp310}"
+TM_PYTHON_VERSIONS="${TM_PYTHON_VERSIONS:-cp38-cp38 cp310-cp310}"
 # Location to store Release wheels
 TM_OUTPUT_DIR="${TM_OUTPUT_DIR:-${this_dir}/wheelhouse}"
 # What "packages to build"