Fix deprecation warning traitsui

[ericpre]

There is currently a traistui deprecation warning when running the test suite:

=============================== warnings summary ===============================
hyperspy_gui_traitsui/tests/test_tools.py::test_image_contrast_tool
hyperspy_gui_traitsui/tests/test_tools.py::test_image_contrast_tool
hyperspy_gui_traitsui/tests/test_tools.py::test_image_contrast_tool
hyperspy_gui_traitsui/tests/test_tools.py::test_image_contrast_tool
  /opt/hostedtoolcache/Python/3.9.12/x64/lib/python3.9/site-packages/traitsui/editor_factory.py:81: DeprecationWarning: Use of format trait is deprecated. Use format_str instead.
    HasPrivateTraits.__init__(self, **traits)

hyperspy_gui_traitsui/tests/test_tools.py::test_image_contrast_tool
  /opt/hostedtoolcache/Python/3.9.12/x64/lib/python3.9/site-packages/traitsui/qt4/extra/bounds_editor.py:44: DeprecationWarning: Use of format trait is deprecated. Use format_str instead.
    self.format = factory.format

Even if this is not obvious where it comes from the traitsui changelog, this deprecation has been introduced in traitsui 7.3.0 (enthought/traitsui#1684) and will be removed in traitsui 8.0.

• Fix deprecation warning form traitsui
• add oldest supported version of dependencies build to github CI
• set minimum requirement of traits (5.0) and traitsui (6.1)
• add changelog entry

[codecov]

Codecov Report

Merging #45 (cb88344) into main (1643210) will increase coverage by 0.37%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #45      +/-   ##
==========================================
+ Coverage   59.65%   60.03%   +0.37%     
==========================================
  Files          16       16              
  Lines         528      533       +5     
  Branches       55       55              
==========================================
+ Hits          315      320       +5     
  Misses        206      206              
  Partials        7        7              

Impacted Files	Coverage Δ
hyperspy_gui_traitsui/tools.py	37.93% <100.00%> (+1.83%)	⬆️

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