Migrate to modern Python Logger API

[emmanuel-ferdman]

Description

This PR resolves the deprecation warnings of the logger library:

DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• Integration tests passed locally by running ./runtests.sh -f -u --net --coverage.
• Quick tests passed locally by running ./runtests.sh --quick --unittests --disttests.
• In-line docstrings updated.
• Documentation updated, tested make html command in the docs/ folder.

[ericspod]

Looks good to me, thanks!