Internal error: AST change with bytes docstring

[konstin]

Black reformats the contents of triple quoted byte strings in docstring position, even though those are not docstrings, causing a crash due to AST changes:

def f():
    b""" a"""

INTERNAL ERROR: Black produced code that is not equivalent to the source.  Please report a bug on https://github.com/psf/black/issues.  This diff might be helpful: /tmp/blk_rb9415ox.log

--- src
+++ dst
@@ -18,11 +18,11 @@
           value=
             Constant(
               kind=
                 None,  # NoneType
               value=
-                b' a',  # bytes
+                b'a',  # bytes
             )  # /Constant
         )  # /Expr
       decorator_list=
       name=
         'f',  # str

$ python3.12
Python 3.12.0 (main, Oct  6 2023, 17:57:44) [GCC 11.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def f():
...     b""" a"""
... 
>>> print(str(f.__doc__))
None

Surprisingly, the empty line rules for class level docstrings look already correct.

Confirmed to occur on 23.10.1 and main (f7cbe4a) with the playground.