gh-139871: Fix 3.15 bytearray.take_bytes example

Currently:
```python
buffer = bytearray(b'abc\ndef')
n = buffer.find(b'\n')
data = bytes(buffer[:n + 1])
del buffer[:n + 1]
assert data == b'abc'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    assert data == b'abc'
           ^^^^^^^^^^^^^^
AssertionError
```

Adding in the `\n` makes the two match:

```python
buffer = bytearray(b'abc\ndef')
n = buffer.find(b'\n')
data = bytes(buffer[:n + 1])
del buffer[:n + 1]
assert data == b'abc\n'
assert buffer == bytearray(b'def')

buffer = bytearray(b'abc\ndef')
n = buffer.find(b'\n')
data = buffer.take_bytes(n + 1)
assert data == b'abc\n'
assert buffer == bytearray(b'def')
```

Author: cmaloney

Doc/whatsnew/3.15.rst

@@ -798,7 +798,7 @@ Other language changes
               n = buffer.find(b'\n')
               data = bytes(buffer[:n + 1])
               del buffer[:n + 1]
-              assert data == b'abc'
+              assert data == b'abc\n'
               assert buffer == bytearray(b'def')
 
         - .. code:: python