Fix test in non-editable installation

[ericpre]

In non-editable installation pytest --pyargs etspy fails with the following error:

From https://github.com/hyperspy/hyperspy-extensions-list/actions/runs/12589744036/job/35090082169

============================= test session starts ==============================
platform linux -- Python 3.12.8, pytest-8.3.4, pluggy-1.5.0
Matplotlib: 3.10.0
Freetype: 2.[12](https://github.com/hyperspy/hyperspy-extensions-list/actions/runs/12589744036/job/35090082169#step:29:13).1
rootdir: /home/runner/work/hyperspy-extensions-list/hyperspy-extensions-list
plugins: mpl-0.17.0, rerunfailures-15.0, xdist-3.6.1
created: 2/2 workers
2 workers [263 items]

...............ss....................................................... [ 27%]
........................................................................ [ 54%]
....ssss.................................................s.............. [ 82%]
...................................ssssssss...F                          [100%]
=================================== FAILURES ===================================
_________________________________ test_version _________________________________
[gw1] linux -- Python 3.12.8 /home/runner/miniconda3/envs/test/bin/python

    def test_version():
        """Test version definition."""
        pyproject = etspy_path.parent / "pyproject.toml"
>       with pyproject.open("rb") as f:

/home/runner/miniconda3/envs/test/lib/python3.12/site-packages/etspy/tests/test_version.py:[13](https://github.com/hyperspy/hyperspy-extensions-list/actions/runs/12589744036/job/35090082169#step:29:14): 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = PosixPath('/home/runner/miniconda3/envs/test/lib/python3.12/site-packages/pyproject.toml')
mode = 'rb', buffering = -1, encoding = None, errors = None, newline = None

    def open(self, mode='r', buffering=-1, encoding=None,
             errors=None, newline=None):
        """
        Open the file pointed to by this path and return a file object, as
        the built-in open() function does.
        """
        if "b" not in mode:
            encoding = io.text_encoding(encoding)
>       return io.open(self, mode, buffering, encoding, errors, newline)
E       FileNotFoundError: [Errno 2] No such file or directory: '/home/runner/miniconda3/envs/test/lib/python3.12/site-packages/pyproject.toml'

/home/runner/miniconda3/envs/test/lib/python3.12/pathlib.py:1013: FileNotFoundError
=============================== warnings summary ===============================
../../../miniconda3/envs/test/lib/python3.12/site-packages/traits/observation/_generated_parser.py:258
../../../miniconda3/envs/test/lib/python3.12/site-packages/traits/observation/_generated_parser.py:258
  /home/runner/miniconda3/envs/test/lib/python3.12/site-packages/traits/observation/_generated_parser.py:258: DeprecationWarning: module 'sre_parse' is deprecated
    import sre_parse

../../../miniconda3/envs/test/lib/python3.12/site-packages/traits/observation/_generated_parser.py:259
../../../miniconda3/envs/test/lib/python3.12/site-packages/traits/observation/_generated_parser.py:259
  /home/runner/miniconda3/envs/test/lib/python3.12/site-packages/traits/observation/_generated_parser.py:259: DeprecationWarning: module 'sre_constants' is deprecated
    import sre_constants

tests/test_utils.py::TestMultiframeAverage::test_register_serialem_stack_multicpu
tests/test_utils.py::TestMultiframeAverage::test_register_serialem_stack_multicpu
  /home/runner/miniconda3/envs/test/lib/python3.12/multiprocessing/popen_fork.py:66: DeprecationWarning: This process (pid=5044) is multi-threaded, use of fork() may lead to deadlocks in the child.
    self.pid = os.fork()

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=========================== short test summary info ============================
FAILED tests/test_version.py::test_version - FileNotFoundError: [Errno 2] No such file or directory: '/home/runner/miniconda3/envs/test/lib/python3.12/site-packages/pyproject.toml'
======= 1 failed, 247 passed, [15](https://github.com/hyperspy/hyperspy-extensions-list/actions/runs/12589744036/job/35090082169#step:29:16) skipped, 6 warnings in 63.61s (0:01:03) =======