Fix a failing test for legacy GMT versions (#3287)

Author: seisman

pygmt/tests/test_datasets_earth_relief.py

@@ -209,4 +209,4 @@ def test_earth_relief_03s_default_registration():
     npt.assert_allclose(data.coords["lon"].data.min(), -10)
     npt.assert_allclose(data.coords["lon"].data.max(), -9.8)
     npt.assert_allclose(data.min(), -2069.85, atol=0.5)
-    npt.assert_allclose(data.max(), -924.5, atol=0.5)
+    npt.assert_allclose(data.max(), -923.5, atol=0.5)