When reformatting a triple-quote string, black fails with an INTERNAL ERROR: Black produced code that is not equivalent to the source

[aaribaud]

Describe the bug

When reformatting a triple-quote string, black fails with an internal error.

To Reproduce

Take this code:

if __name__ == "__main__":
    """     This string...
    ... will confuse black.
    
    """
    pass

And run it with these arguments:

$ black file.py

The resulting error is:

error: cannot format blackerrdemo.py: 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_d030my1_.log

Oh no! 💥 💔 💥
1 file failed to reformat.

Expected behavior

Black should leave the string untouched or, if it decides to reformat it, reformat it without failure.

Environment

• Black's version: [24.3.0 (compiled: yes), 24.3.1.dev5+gc9d2635 (compiled: no)]
• OS and Python version: [Debian Linux 12 (Bookworm)/Python 3.11.2]

Additional context

Reproduced with branch main at commit c9d2635