[Snyk] Security upgrade python from 3.9.11-alpine to 3.9-alpine

[snyk-bot]

Keeping your Docker base image up-to-date means you’ll benefit from security fixes in the latest version of your chosen image.

Changes included in this PR

• Dockerfile

We recommend upgrading to python:3.9-alpine, as this image has only 0 known vulnerabilities. To do this, merge this pull request, then verify your application still works as expected.

Some of the most important vulnerabilities in your base image include:

Severity	Priority Score / 1000	Issue	Exploit Maturity
	500	CVE-2022-28391 SNYK-ALPINE315-BUSYBOX-2440607	No Known Exploit
	500	CVE-2022-28391 SNYK-ALPINE315-BUSYBOX-2440607	No Known Exploit
	150	ALPINE-13661 SNYK-ALPINE315-BUSYBOX-2606932	No Known Exploit
	150	ALPINE-13661 SNYK-ALPINE315-BUSYBOX-2606932	No Known Exploit
	400	Out-of-bounds Write SNYK-ALPINE315-ZLIB-2434420	No Known Exploit

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[mcdonnnj]

We use full version numbers for our Python Docker image tags e.g. 3.9.16-alpine vs 3.9-alpine.