build: Bump python from 3.9.5-slim-buster to 3.9.6-slim-buster (#12)

Bumps python from 3.9.5-slim-buster to 3.9.6-slim-buster.

---
updated-dependencies:
- dependency-name: python
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Dockerfile

@@ -1,5 +1,5 @@
 # TODO: Find out whether it possible to use "faster" base Python image
-FROM python:3.9.5-slim-buster as python-base
+FROM python:3.9.6-slim-buster as python-base
 
 LABEL maintainer="Igor Davydenko <iam@igordavydenko.com>"
 LABEL description="Add poetry, pre-commit, and other dev-tools to official Python slim Docker image."