Relax python six dependency to allow 1.16

[BioGeek]

Changelog: Fix: Relax python six dependency to allow 1.16
Docs: Omit

The diff between six-1.15.0 and six-1.16.0 only contains some fixes to support Python 3.10 (fixes issues #341, #343 and #349) and shouldn't affect any conan logic.

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^{Note: By default this PR will skip the slower tests and will use a limited set of python versions. Check here how to increase the testing level by writing some tags in the current PR body text.}

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