Fix failing image scalebar export test

[ericpre]

Fix for failure with matplotlib development version - from https://github.com/hyperspy/hyperspy-extensions-list/actions/runs/12849344100/job/35838748193:

=================================== FAILURES ===================================
__________________________ test_export_scalebar[gif] ___________________________
[gw0] linux -- Python 3.12.8 /home/runner/miniconda3/envs/test/bin/python

ext = 'gif'
tmp_path = PosixPath('/tmp/pytest-of-runner/pytest-1/popen-gw0/test_export_scalebar_gif_0')

    @pytest.mark.skipif(
        Version(imageio.__version__) < Version("2.23"),
        reason="needs imageio >=2.23",
    )
    @pytest.mark.parametrize(("ext"), ["png", "bmp", "gif", "jpg"])
    def test_export_scalebar(ext, tmp_path):
        hs = pytest.importorskip("hyperspy.api", reason="hyperspy not installed")
        pytest.importorskip("matplotlib_scalebar")
        # Use np.uint8 to be able to save as BMP
        pixels = 64
        data = np.arange(pixels**2).reshape((pixels, pixels)).astype(np.uint8)
        s = hs.signals.Signal2D(data)
        s.axes_manager[0].units = "nm"
        s.axes_manager[1].units = "nm"
    
        filename = tmp_path / f"test_scalebar_export.{ext}"
        if ext in ["bmp", "gif"]:
>           with pytest.raises(ValueError):
E           Failed: DID NOT RAISE <class 'ValueError'>

../../../miniconda3/envs/test/lib/python3.12/site-packages/rsciio/tests/test_image.py:118: Failed

Progress of the PR

• Replace hardcoded list with supported file types from matplotlib,
• [n/a] update docstring (if appropriate),
• [n/a] update user guide (if appropriate),
• [n/a] add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• [n/a] Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:rosettasciio build of this PR (link in github checks)
• update tests,
• ready for review.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.84%. Comparing base (8a420af) to head (a003297).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #359   +/-   ##
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  Coverage   87.84%   87.84%           
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  Files          85       85           
  Lines       11246    11246           
  Branches     2084     2084           
=======================================
  Hits         9879     9879           
  Misses        868      868           
  Partials      499      499           

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