Update test

Author: brianschubert

test-data/unit/check-tuples.test

@@ -1440,8 +1440,8 @@ t[y:]  # E: Slice index must be an integer, SupportsIndex or None
 
 [case testTupleSliceStepZeroNoCrash]
 # This was crashing: https://github.com/python/mypy/issues/18062
-# TODO: emit better error when 0 is used for step
-()[::0]  # E: Ambiguous slice of a variadic tuple
+()[::0]  # E: Ambiguous slice of a variadic tuple \
+         # E: Slice step cannot be 0
 [builtins fixtures/tuple.pyi]
 
 [case testInferTupleTypeFallbackAgainstInstance]