Add brackets to force separator to also exist in the split

Author: andy31415

scripts/py_matter_yamltests/matter_yamltests/parser.py

@@ -1225,7 +1225,7 @@ def _config_variable_substitution(self, value):
             # But some other tests were relying on the fact that the expression was put 'as if' in
             # the generated code and was resolved before being sent over the wire. For such
             # expressions (e.g 'myVar + 1') we need to compute it before sending it over the wire.
-            tokens = re.split("[- ()|+*/%]", value)
+            tokens = re.split("([- ()|+*/%])", value)
             if len(tokens) == 0:
                 return value