Python 3.11 compatibility

[mirekdlugosz]

After adding Python 3.11 to CI versions, run failed:

Traceback (most recent call last):
  File "/home/runner/.cache/pypoetry/virtualenvs/pelican-liquid-tags-aUA_7FYk-py3.11/bin/invoke", line 8, in <module>
    sys.exit(program.run())
             ^^^^^^^^^^^^^
  File "/home/runner/.cache/pypoetry/virtualenvs/pelican-liquid-tags-aUA_7FYk-py3.11/lib/python3.11/site-packages/invoke/program.py", line 373, in run
    self.parse_collection()
  File "/home/runner/.cache/pypoetry/virtualenvs/pelican-liquid-tags-aUA_7FYk-py3.11/lib/python3.11/site-packages/invoke/program.py", line 465, in parse_collection
    self.load_collection()
  File "/home/runner/.cache/pypoetry/virtualenvs/pelican-liquid-tags-aUA_7FYk-py3.11/lib/python3.11/site-packages/invoke/program.py", line 699, in load_collection
    module, parent = loader.load(coll_name)
                     ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/.cache/pypoetry/virtualenvs/pelican-liquid-tags-aUA_7FYk-py3.11/lib/python3.11/site-packages/invoke/loader.py", line 76, in load
    module = imp.load_module(name, fd, path, desc)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/hostedtoolcache/Python/3.11.0/x64/lib/python3.11/imp.py", line 235, in load_module
    return load_source(name, filename, file)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/hostedtoolcache/Python/3.11.0/x64/lib/python3.11/imp.py", line 172, in load_source
    module = _load(spec)
             ^^^^^^^^^^^
  File "<frozen importlib._bootstrap>", line 721, in _load
  File "<frozen importlib._bootstrap>", line 690, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 940, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/home/runner/work/liquid-tags/liquid-tags/tasks.py", line 25, in <module>
    @task
     ^^^^
  File "/home/runner/.cache/pypoetry/virtualenvs/pelican-liquid-tags-aUA_7FYk-py3.11/lib/python3.11/site-packages/invoke/tasks.py", line 331, in task
    return klass(args[0], **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/.cache/pypoetry/virtualenvs/pelican-liquid-tags-aUA_7FYk-py3.11/lib/python3.11/site-packages/invoke/tasks.py", line 76, in __init__
    self.positional = self.fill_implicit_positionals(positional)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/.cache/pypoetry/virtualenvs/pelican-liquid-tags-aUA_7FYk-py3.11/lib/python3.11/site-packages/invoke/tasks.py", line 167, in fill_implicit_positionals
    args, spec_dict = self.argspec(self.body)
                      ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/.cache/pypoetry/virtualenvs/pelican-liquid-tags-aUA_7FYk-py3.11/lib/python3.11/site-packages/invoke/tasks.py", line 153, in argspec
    spec = inspect.getargspec(func)
           ^^^^^^^^^^^^^^^^^^
AttributeError: module 'inspect' has no attribute 'getargspec'. Did you mean: 'getargs'?
Error: Process completed with exit code 1.

This issue needs to be investigated and fixed.