test: Remove python3.8 from integ tests

[valerena]

We removed support for python3.8 in AppVeyor instances.

The runtime is deprecated in Lambda already, but it's still partially supported (that's why we're not removing it completely)

There are still some unit tests using python3.8, that we can remove those in the future.

Which issue(s) does this change fix?

Test failures

Why is this change necessary?

Our AppVeyor instances that run integration tests don't have Python3.8 configured anymore.

How does it address the issue?

We don't run the integration tests that need to use python3.8 in the environment.

What side effects does this change have?

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[seshubaws]

some lint error

mypy --exclude /testdata/ --exclude /init/templates/ --no-incremental setup.py samcli tests schema
tests/unit/local/docker/test_lambda_image.py:338: error: closing parenthesis ')' does not match opening parenthesis '[' on line 336  [syntax]
Found 1 error in 1 file (errors prevented further checking)
make: *** [lint] Error 2