Simplify common_type_error validation logic

As per feedback in #447

Author: amoeba

numpydoc/validate.py

@@ -584,15 +584,8 @@ def validate(obj_name):
                     ("string", "str"),
                 ]
                 for wrong_type, right_type in common_type_errors:
-                    param_type = doc.parameter_type(param)
-                    if wrong_type in param_type:
-                        # Ignore if wrong_type is used as a substring
-                        if (
-                            re.match(f"\w+{wrong_type}", param_type) or
-                            re.match(f"{wrong_type}\w+", param_type)
-                           ):
-                            continue
-
+                    if wrong_type in set(re.split(r"\W", doc.parameter_type(
+                            param))):
                         errs.append(
                             error(
                                 "PR06",