Fix invalid escape sequence flagged by pytest

```
pythonosc/dispatcher.py:153
  /workspaces/python-osc/pythonosc/dispatcher.py:153: DeprecationWarning: invalid escape sequence '\+'
    pattern = pattern.replace('\\*', '[\\w|\+]*')
```

Author: attwad

pythonosc/dispatcher.py

@@ -150,7 +150,7 @@ def handlers_for_address(self, address_pattern: str) -> Generator[Handler, None,
         pattern = escaped_address_pattern.replace('\\?', '\\w?')
         # '*' in the OSC Address Pattern matches any sequence of zero or more
         # characters.
-        pattern = pattern.replace('\\*', '[\w|\+]*')
+        pattern = pattern.replace('\\*', '[\\w|\\+]*')
         # The rest of the syntax in the specification is like the re module so
         # we're fine.
         pattern = pattern + '$'