REL: v3.6.3

This is the third bugfix release of the 3.6.x series.

This release contains several bug-fixes and adjustments:

• Fix Artist removal from axes_grid1 Axes classes
• Fix inset_locator in subfigures
• Fix scatter on masked arrays with units
• Fix colorbar ticks with log norm contours
• Fix deprecation warnings in GTK4 backend
• Fix using relative paths in HTMLWriter
• Improve failure message from rcParams string validation for tuple inputs
• Improve performance of QtAgg backends
• No longer modify pil_kwargs argument to imsave and savefig