[WIP] Remove Python 3.8 targets from Actions

[jrmccluskey]

Python 3.8 is scheduled to reach EOL in October of 2024. This PR removes actions targets for 3.8 ahead of the removal of Beam support for 3.8.

DO NOT MERGE

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[jrmccluskey]

The coverage failure is because the runner isn't picking up the change to the action but it is picking up the configuration change to make python 3.9 the default. As a result, the workflow is attempting to start a 3.8 virtualenv but doesn't have 3.8 in the environment and this is causing a failure. The new action :sdks:python:test-suites:tox:py39:preCommitPyCoverage is executing properly in local runs