Update circleci/python Docker tag to v3.9

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
circleci/python	docker	minor	3.8 -> 3.9
circleci/python	docker	minor	3.7 -> 3.9
circleci/python	docker	minor	3.6 -> 3.9
circleci/python	docker	minor	3.5 -> 3.9

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Configuration

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[coveralls]

Coverage remained the same at 95.802% when pulling 75c90a0 on renovate/circleci-python-3.x into 14204af on master.

[coveralls]

Coverage remained the same at 95.802% when pulling 75c90a0 on renovate/circleci-python-3.x into 14204af on master.

[renovate]

Renovate Ignore Notification

As this PR has been closed unmerged, Renovate will now ignore this update (3.9). You will still receive a PR once a newer version is released, so if you wish to permanently ignore this dependency, please add it to the ignoreDeps array of your renovate config.

If this PR was closed by mistake or you changed your mind, you can simply rename this PR and you will soon get a fresh replacement PR opened.