Have pytest.raises match against exception __notes__ (#11227)

The doctest is skipped because add_note is only available in 3.11,

Closes #11223

src/_pytest/python_api.py

@@ -843,6 +843,14 @@ def raises(  # noqa: F811
         >>> with pytest.raises(ValueError, match=r'must be \d+$'):
         ...     raise ValueError("value must be 42")
 
+    The ``match`` argument searches the formatted exception string, which includes any
+    `PEP-678 <https://peps.python.org/pep-0678/>` ``__notes__``:
+
+        >>> with pytest.raises(ValueError, match=r'had a note added'):  # doctest: +SKIP
+        ...    e = ValueError("value must be 42")
+        ...    e.add_note("had a note added")
+        ...    raise e
+
     The context manager produces an :class:`ExceptionInfo` object which can be used to inspect the
     details of the captured exception::