grass.gunittest: Fix typo in function TestCase.assertVectorsNoAreaDifference() for _compute_vector_xor (#6125)

Author: echoix

python/grass/gunittest/case.py

@@ -1127,7 +1127,7 @@ def assertVectorsNoAreaDifference(
 
         This method should not be used to test v.overlay or v.select.
         """
-        diff = self._compute_xor_vectors(
+        diff = self._compute_vector_xor(
             ainput=reference,
             binput=actual,
             alayer=layer,