fix for mounted apps

Interpolate request.script_name for openapi path_pattern to accomodate

pyramid_openapi3/wrappers.py

@@ -36,10 +36,19 @@ def path(self) -> str:
     @property
     def path_pattern(self) -> str:
         """The matched url with path pattern."""  # noqa D401
+
+        # since application might be mounted on virtual location we need
+        # to prepend it to the route pattern, or request's response validation
+        # will fail. one example of this is using WSGI compositors like
+        # rutter (https://rutter.rtfd.io)
+        # see:  https://wsgi.readthedocs.io/en/latest/definitions.html#envvar-SCRIPT_NAME
+        relative_matched_route_pattern = "%s%s" % \
+            (self.request.script_name, self.request.matched_route.pattern)
+
         path_pattern = (
-            self.request.matched_route.pattern
+            relative_matched_route_pattern
             if self.request.matched_route
-            else self.request.path_info
+            else self.request.path
         )
         return path_pattern