Log Message:
py-cairo: update to 1.21.0.

1.21.0 - 2022-03-07
-------------------

* Require Python 3.7+ :pr:`250`
* Require meson 0.53+
* Using `setup.py` directly to build/install pycairo is deprecated.
  Use meson instead.
* `setup.py` now requires setuptools. Previously it was optional.
* The complete API reference is now included in the typing stubs, so it can be \ 
consumed/shown by IDEs. :pr:`236` :pr:`252`