REL: v3.4.2

This is the second bugfix release of the 3.4.x series.

This release contains several critical bug-fixes:

• Generate wheels usable on older PyPy7.3.{0,1}
• Fix compatibility with Python 3.10
• Add subplot_mosaic Axes in the order the user gave them to us
• Correctly handle 'none' facecolors in do_3d_projection
• Ensure that Matplotlib is importable even if there's no HOME
• Fix CenteredNorm with halfrange
• Fix bar_label for bars with NaN values
• Fix clip paths when zoomed such that they are outside the figure
• Fix creation of RangeSlider with valinit
• Fix handling of "d" glyph in backend_ps, fixing EPS output
• Fix handling of datetime coordinates in pcolormesh with Pandas
• Fix processing of some errorbar arguments
• Fix removal of shared polar Axes
• Fix resetting grid visibility
• Fix subfigure indexing error and tight bbox
• Fix textbox cursor color
• Fix TkAgg event loop error on window close
• Ignore errors for sip with no setapi (Qt4Agg import errors)