Support Python 3.12

[rad-pat]

With Python 3.12 the following error is encountered:

  Traceback (most recent call last):
    File "/opt/hostedtoolcache/Python/3.12.2/x64/bin/liccheck", line 5, in <module>
      from liccheck.command_line import main
    File "/opt/hostedtoolcache/Python/3.12.2/x64/lib/python3.12/site-packages/liccheck/command_line.py", line 5, in <module>
      from liccheck.requirements import parse_requirements, resolve, resolve_without_deps
    File "/opt/hostedtoolcache/Python/3.12.2/x64/lib/python3.12/site-packages/liccheck/requirements.py", line 1, in <module>
      import pkg_resources
  ModuleNotFoundError: No module named 'pkg_resources'

#114 covers the same error as a deprecation warning, but full support should be given to Python 3.12