Bump poetry version to 1.6.1

What does this merge request do and why?

This MR bumps Poetry from 1.5.1 to 1.6.1. Beside bug fixes and other improvements, I am excited to see some performance improvements with poetry install.

rm -rf .venv
time poetry install

# Poetry 1.5.1
--snip--
Executed in    5.22 secs    fish           external
   usr time    3.33 secs    0.34 millis    3.33 secs
   sys time    2.75 secs    2.14 millis    2.75 secs

# Poetry 1.6.1
--snip--
Executed in    4.08 secs    fish           external
   usr time    2.96 secs    0.05 millis    2.96 secs
   sys time    2.70 secs    2.02 millis    2.70 secs

See the full change log https://github.com/python-poetry/poetry/compare/1.5.1...1.6.1

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.