Fix the dpi related cron job failures

[aaronayres35]

There was a recent pillow release which included this change: python-pillow/Pillow#5476
That was causing the cron job to fail with:

======================================================================
FAIL: test_save_dpi (kiva.tests.test_agg_drawing.TestAggDrawing)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.8.11/x64/lib/python3.8/site-packages/kiva/tests/test_agg_drawing.py", line 24, in test_save_dpi
    self.assertEqual(self.save_and_return_dpi(), 144)
AssertionError: 143.99259999999998 != 144

======================================================================
FAIL: test_save_dpi (kiva.tests.test_celiagg_drawing.TestCeliaggDrawing)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.8.11/x64/lib/python3.8/site-packages/kiva/tests/test_celiagg_drawing.py", line 22, in test_save_dpi
    self.assertEqual(self.save_and_return_dpi(), 144)
AssertionError: 143.99259999999998 != 144

----------------------------------------------------------------------

This PR simply adjusts for this by adding an int() call when we get the dpi. Note the above pillow PR explains why this started occurring.

fixes #866

[aaronayres35]

I've manually triggered the cron job on this branch to verify this fix: https://github.com/enthought/enable/actions/runs/1045927150

EDIT: ah and it doesn't fix it! int(143.99259999999998) is 143. using round does what we expect.
new run with round: https://github.com/enthought/enable/actions/runs/1046114933

[rahulporuri]

LGTM