Mark test_binstats_quantile as xfail in the GMT Legacy Tests workflow (#4087)

GMT 6.4 gives different results to GMT 6.5+ for binstats quantile statistic,
xref GenericMappingTools/gmt#8243

Author: weiji14

pygmt/tests/test_binstats.py

@@ -6,7 +6,9 @@
 
 import numpy.testing as npt
 import pytest
+from packaging.version import Version
 from pygmt import binstats
+from pygmt.clib import __gmt_version__
 from pygmt.enums import GridRegistration, GridType
 from pygmt.helpers import GMTTempFile
 
@@ -51,6 +53,11 @@ def test_binstats_no_outgrid():
     npt.assert_allclose(temp_grid.mean(), 4227489)
 
 
+# TODO(GMT>=6.5.0): Remove the xfail marker for the upstream bug fixed in GMT 6.5.0.
+@pytest.mark.xfail(
+    condition=Version(__gmt_version__) < Version("6.5.0"),
+    reason="Upstream bug fixed in https://github.com/GenericMappingTools/gmt/pull/8243",
+)
 def test_binstats_quantile():
     """
     Test binstats quantile statistic functionality.
@@ -67,6 +74,7 @@ def test_binstats_quantile():
     assert temp_grid.dims == ("y", "x")
     assert temp_grid.gmt.gtype is GridType.CARTESIAN
     assert temp_grid.gmt.registration is GridRegistration.GRIDLINE
+    assert temp_grid.dtype == "float32"
     npt.assert_allclose(temp_grid.max(), 15047685)
     npt.assert_allclose(temp_grid.min(), 53)
     npt.assert_allclose(temp_grid.median(), 543664.5)