ci: Conflict between poetry 1.1.x and python 3.5

[btorresgil]

Describe the bug

Cannot upgrade CI to use poetry higher than 1.0. When using 1.1, a deprecation messages seems to prevent collection of the poetry cache path which causes the cache step to file because no path is provided.

Example: https://github.com/PaloAltoNetworks/pan-os-python/runs/1166935375?check_suite_focus=true

Expected behavior

All tests should pass.

Current behavior

Python 3.5 tests fail. Other tests are skipped due to the failures.

Possible solution

Unknown at this time, need to do more experimenting with poetry 1.1 and python 3.5.

Context

This affects the GitHub Actions CI tests only.