Update python Docker tag

[renovate-bot]

This PR contains the following updates:

Package	Type	Update	Change
python	final	minor	3.6.0 -> 3.8.0b1
python	final	minor	3.7 -> 3.8

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[leahecole]

@averikitsch let me know how you feel about the files that you're an owner of (I'm guessing those are the run ones?) If you're not ready for 3.8 yet that's totally fine

[averikitsch]

Though we don't have full testing for these samples, they should be fine to update. Though tagging @dinagraves for some test failures.

[dinagraves]

3.5 and 2.7 fail b/c of the f-strings. This is expected - as long as it passes on 3.6 and above, it's fine.

[leahecole]

(Edited - upon further reading I think it's fine to update the custom dockerfiles for appengine + cloudsql) I can address the trace ones if needed, @ZiweiZhao and @DukeNg

[leahecole]

@dinagraves - I added you as a formal reviewer - +1 on the tests - i actually have another PR out rn hoping to fix the CI/CD so it doesn't run on those - if you or @averikitsch could give it the formal approve at some point, that would be much appreciated