Fix MarkerStyle for matplotlib compatibility

[rbuckland]

this single change allows qiskit_experiments to work for matplotlib 3.7

venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/__init__.py:68: in <module>
    from . import library
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/library/__init__.py:116: in <module>
    from .calibration import (
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/library/calibration/__init__.py:62: in <module>
    from .rough_frequency import RoughFrequencyCal
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/library/calibration/rough_frequency.py:20: in <module>
    from qiskit_experiments.library.characterization.qubit_spectroscopy import QubitSpectroscopy
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/library/characterization/__init__.py:79: in <module>
    from .analysis import (
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/library/characterization/analysis/__init__.py:15: in <module>
    from .drag_analysis import DragCalAnalysis
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/library/characterization/analysis/drag_analysis.py:20: in <module>
    import qiskit_experiments.curve_analysis as curve
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/curve_analysis/__init__.py:553: in <module>
    from .base_curve_analysis import BaseCurveAnalysis
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/curve_analysis/base_curve_analysis.py:31: in <module>
    from qiskit_experiments.visualization import (
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/visualization/__init__.py:71: in <module>
    from .drawers import BaseDrawer, LegacyCurveCompatDrawer, MplDrawer
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/visualization/drawers/__init__.py:15: in <module>
    from .legacy_curve_compat_drawer import LegacyCurveCompatDrawer
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/visualization/drawers/legacy_curve_compat_drawer.py:20: in <module>
    from qiskit_experiments.curve_analysis.visualization import BaseCurveDrawer
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/curve_analysis/visualization/__init__.py:25: in <module>
    from .mpl_drawer import MplCurveDrawer
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/curve_analysis/visualization/mpl_drawer.py:36: in <module>
    class MplCurveDrawer(BaseCurveDrawer):
venvs/s/581f024a/venv/lib/python3.9/site-packages/qiskit_experiments/curve_analysis/visualization/mpl_drawer.py:39: in MplCurveDrawer
    DefaultMarkers = MarkerStyle().filled_markers
venvs/s/581f024a/venv/lib/python3.9/site-packages/matplotlib/markers.py:261: in __init__
    _api.warn_deprecated(
venvs/s/581f024a/venv/lib/python3.9/site-packages/matplotlib/_api/deprecation.py:96: in warn_deprecated
    warn_external(warning, category=MatplotlibDeprecationWarning)
venvs/s/581f024a/venv/lib/python3.9/site-packages/matplotlib/_api/__init__.py:388: in warn_external
    warnings.warn(message, category, stacklevel)
E   matplotlib._api.deprecation.MatplotlibDeprecationWarning: Calling MarkerStyle() with no parameters is deprecated since 3.6; support will be removed two minor releases later.  Use MarkerStyle('') to construct an empty MarkerStyle.

Summary

matplotlib API changes in 3.7

Details and comments

Some details that should be in this section include:

qiskit_experiments has a warning if this change it not made.

• E matplotlib._api.deprecation.MatplotlibDeprecationWarning: Calling MarkerStyle() with no parameters is deprecated since 3.6; support will be removed two minor releases later. Use MarkerStyle('') to construct an empty MarkerStyle.

PR checklist (delete when all criteria are met)

• I have read the contributing guide CONTRIBUTING.md.
• I have added the tests to cover my changes.
• I have updated the documentation accordingly.
• I have added a release note file using reno if this change needs to be documented in the release notes.

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[ihincks]

I closed a competing PR (#1130) in favour of just pushing this one through (@coruscating).
Here's a patch for a release note if you want it:

diff --git a/releasenotes/notes/mpl-36-markerstyle-c6b51652b08991a5.yaml b/releasenotes/notes/mpl-36-markerstyle-c6b51652b08991a5.yaml
new file mode 100644
index 0000000..eeb5e8e
--- /dev/null
+++ b/releasenotes/notes/mpl-36-markerstyle-c6b51652b08991a5.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Removed no-argument construction of `matplotlib.markers.MarkerStyle` for
+    [compatibility with matplotlib>=3.6](https://matplotlib.org/stable/api/prev_api_changes/api_changes_3.6.0.html#positional-keyword-arguments).

[coruscating]

@rbuckland Thanks for contributing. Can you sign the CLA?

[rbuckland]

Done

[coruscating]

@rbuckland What do you think about the proposed change? We'd like to include this in the next bug fix release in the next week or two, and if you can write a short release note describing the fix, that would be great.

[coruscating]

@rbuckland Unless you have objections, I will update this PR with @ihincks's proposed changes and the release note.