chaco.downsample test_linear fail on macOS

[itziakos]

We started seeing these errors on macOS again.

======================================================================
FAIL: test_linear (chaco.downsample.tests.test_lttb.TestLargestTriangleThreeBuckets.test_linear)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/runner/.edm/envs/chaco-test-3.11-pyside6/lib/python3.11/site-packages/chaco/downsample/tests/test_lttb.py", line 56, in test_linear
    assert_almost_equal(
  File "/Users/runner/.edm/envs/chaco-test-3.11-pyside6/lib/python3.11/site-packages/numpy/testing/_private/utils.py", line 611, in assert_almost_equal
    return assert_array_almost_equal(actual, desired, decimal, err_msg)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/runner/.edm/envs/chaco-test-3.11-pyside6/lib/python3.11/site-packages/numpy/_utils/__init__.py", line 86, in wrapper
    return fun(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^
  File "/Users/runner/.edm/envs/chaco-test-3.11-pyside6/lib/python3.11/site-packages/numpy/testing/_private/utils.py", line 1172, in assert_array_almost_equal
    assert_array_compare(compare, actual, desired, err_msg=err_msg,
  File "/Users/runner/.edm/envs/chaco-test-3.11-pyside6/lib/python3.11/site-packages/numpy/testing/_private/utils.py", line 921, in assert_array_compare
    raise AssertionError(msg)
AssertionError: 
Arrays are not almost equal to 7 decimals

Mismatched elements: 20 / 24 (83.3%)
Max absolute difference among violations: 0.8
Max relative difference among violations: 5.
 ACTUAL: array([[ 0. ,  0. ],
       [ 0.6,  0.6],
       [ 1.8,  1.8],...
 DESIRED: array([[ 0. ,  0. ],
       [ 0.1,  0.1],
       [ 1. ,  1. ],...