Always pass integers to wx.Size.

[QuLogic]

PR Summary

Fixes test failure on Python 3.10, https://bugzilla.redhat.com/show_bug.cgi?id=1902382

PR Checklist

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (run flake8 on changed files to check).
• [n/a] New features are documented, with examples if plot related.
• [n/a] Documentation is sphinx and numpydoc compliant (the docs should build without error).
• Conforms to Matplotlib style conventions (install flake8-docstrings and run flake8 --docstring-convention=all).
• [n/a] New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• [n/a] API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).

[tacaswell]

Why ceil instead of floor?

[anntzer]

Why ceil instead of floor?

(It would be nice to document once and for all how floating-point canvas sizes (which can legitimately occur e.g. with vector backends) are supposed to be handled by backends that only support integer sizes (typically raster backends).)

[QuLogic]

Because that's what's already done here:

matplotlib/lib/matplotlib/backends/backend_wx.py

Lines 505 to 508 in ff15ca9

	FigureCanvasBase.__init__(self, figure)
	w, h = map(math.ceil, figure.bbox.size)
	# Set preferred window size hint - helps the sizer, if one is connected
	wx.Panel.__init__(self, parent, id, size=wx.Size(w, h))

[QuLogic]

@meeseeksdev backport to v3.3.x