Python 3.6 is not available on ubuntu-latest (22.04).
It was available when ubuntu-latest was 20.04.

Remove Python 3.6 from tests to fix tests

Python 3.7 is EOL, and updated versions of some dependencies, such as
pylint 3, only support Python 3.8+. Drop Python 3.7 in preparation to
update those dependencies, which in turn should enable support for
Python 3.11 and 3.12.

Update first-party GitHub Actions to avoid warnings about node12 and
node16.
 * Update actions/checkout from v1 to v4
 * Update actions/setup-python from v2/v3 to v5

Update first-party GitHub Actions

Drop Python 3.7 and support only Python 3.8+

When trying to add Python 3.11 and 3.12, tests failed due to a
dependency chain issue with the chain starting at pylint and ending at
an outdated version of wrapt that did not support Python 3.11+. The
earliest version of pylint with an updated version of wrapt is pylint
2.15. However, pylint 3.1.0 is the current version, so use that instead.

Update pylint from 2.12.1 to 3.1.0

Add Python 3.11 and 3.12

Also, update the README to just point to requirements.txt.

Using different macos versions for python older and newer than 3.11

- New parameter use-external-python to use an already installed python
- Installation of requirements.txt uses --ignore-installed to avoid overriding versions defined in an external python
- Adding a test workflow to check use-external-python

Resolves #15 Allow to use an external python module

Update all requirements to latest versions

Fixes #19 Updating README and adding an example for use-external-python