tests: make pint test for dimensionless safe

tests/data/test_cf_units.py

@@ -23,9 +23,11 @@ class TestCfUnits(unittest.TestCase):
         self.assertEqual(u("degC"), "°C")
         self.assertEqual(u("degree_Celsius"), "°C")
 
-        self.assertEqual(u(""), "1")
-        self.assertEqual(u("1"), "1")
-        self.assertEqual(u("m/m"), "1")
+        # "dimensionless" representation inconsistent across different pint versions
+        # will be "1" for newer versions (>=0.24.1) to be in line with cf-conventions
+        self.assertTrue(u("") in ("1", "dimensionless", ""))
+        self.assertTrue(u("1") in ("1", "dimensionless", ""))
+        self.assertTrue(u("m/m") in ("1", "dimensionless", ""))
 
         self.assertEqual(u("m/s"), "m s-1")
         self.assertEqual(u("m s-1"), "m s-1")