not compatible with upcoming `invoke` release

Start with rellu/init.py and utest/test_version.py, then reproduce the collection failure with pytest. Inspect how the project imports and checks Invoke's version, and verify that the test suite collects and passes with the upcoming Invoke release.

Hi,

After finding a serious problem with the latest release of invoke (2.2.1): https://github.com/pyinvoke/invoke/issues/1054, I had to package the unreleased git tree.

EDIT: The issue was not in invoke; the latest 2.2.1 release is fine. The rest of this issue still holds for a future release.

There seems to be a small incompatibility with rellu, which is found when running its test suite:

============================= test session starts ==============================
platform linux -- Python 3.11.11, pytest-8.4.1, pluggy-1.6.0 -- /gnu/store/v76lvm9985mj5h3kwrkif7gnqv3q30ck-python-wrapper-3.11.11/bin/python
cachedir: .pytest_cache
hypothesis profile 'default'
rootdir: /tmp/guix-build-python-rellu-0.7.drv-0/source
plugins: hypothesis-6.135.26
collecting ... collected 0 items / 1 error

==================================== ERRORS ====================================
____________________ ERROR collecting utest/test_version.py ____________________
ImportError while importing test module '/tmp/guix-build-python-rellu-0.7.drv-0/source/utest/test_version.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/gnu/store/lawd7nyacmw4f5as1mlzv2zigjwm03y5-python-rellu-0.7/lib/python3.11/site-packages/rellu/__init__.py:36: in <module>
    from invoke import __version_info__ as invoke_version
E   ImportError: cannot import name '__version_info__' from 'invoke' (/gnu/store/vkqlzpr6vd4hh0lvkj8im3b3d7s6mjih-python-invoke-2.2.1-0.ba193d1/lib/python3.11/site-packages/invoke/__init__.py)

During handling of the above exception, another exception occurred:
/gnu/store/f3sc2n63n727bysn4040gsk5gsh2502w-python-pytest-8.4.1/lib/python3.11/site-packages/_pytest/python.py:498: in importtestmodule
    mod = import_path(
/gnu/store/f3sc2n63n727bysn4040gsk5gsh2502w-python-pytest-8.4.1/lib/python3.11/site-packages/_pytest/pathlib.py:587: in import_path
    importlib.import_module(module_name)
/gnu/store/1qmk0ip6gvjs9i9pwj74n4yddqcl45rg-python-3.11.11/lib/python3.11/importlib/__init__.py:126: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
<frozen importlib._bootstrap>:1204: in _gcd_import
    ???
<frozen importlib._bootstrap>:1176: in _find_and_load
    ???
<frozen importlib._bootstrap>:1147: in _find_and_load_unlocked
    ???
<frozen importlib._bootstrap>:690: in _load_unlocked
    ???
/gnu/store/f3sc2n63n727bysn4040gsk5gsh2502w-python-pytest-8.4.1/lib/python3.11/site-packages/_pytest/assertion/rewrite.py:186: in exec_module
    exec(co, module.__dict__)
utest/test_version.py:5: in <module>
    from rellu.version import Version
/gnu/store/lawd7nyacmw4f5as1mlzv2zigjwm03y5-python-rellu-0.7/lib/python3.11/site-packages/rellu/__init__.py:41: in <module>
    raise ImportError('invoke 0.20 or newer required.')
E   ImportError: invoke 0.20 or newer required.
=========================== short test summary info ============================
ERROR utest/test_version.py
!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!
=============================== 1 error in 0.33s ===============================