REL: v3.3.4
This is the fourth bugfix release of the 3.3.x series.
This release contains several critical bug-fixes:
* Fix WebAgg initialization.
* Fix parsing QT_API setting with mixed case.
* Fix build with LTO disabled in environment.
* Fix test compatibility with Python 3.10.
* Fix test compatibility with NumPy 1.20.
* Fix test compatibility with pytest 6.2.
