CI pipeline does not seem to be testing against corresponding Python versions

[YaraslauZhylko]

The CI GitHub Actions jobs are supposed to run the tests against the dedicated Python version.
But it seems that they still use the version provided by the image.

Some tests that were supposed to fail under Python 3.7 and 3.8 did not fail: https://github.com/redis/redis-om-python/actions/runs/4076674172/jobs/7024748452

[YaraslauZhylko]

PR with a fix: #479