Help messages with dunders are rendered as bold instead of displaying literal `__`

[zanieb]

Help messages with content that includes __XXXX__ is rendered bold instead of displaying the __ which is common for dunder variables.

example.py:1:22: F401 [*] `.version.__version__` imported but unused
  |
1 | from .version import __version__
  |                      ^^^^^^^^^^^ F401
  |
  = help: Remove unused import: `.version.version`

Found 1 error.
[*] 1 potentially fixable with the --fix option.

or

example.pyi:3:32: PYI016 Duplicate union member `Literal["__test__"]`
  |
1 | from typing import Literal, Union

2 | 
3 | x = Union[Literal["__test__"], Literal["__test__"]]
  |                                ^^^^^^^^^^^^^^^^^^^ PYI016
  |
  = help: Remove duplicate union member `Literal["test"]`

Originally reported in #5697 (comment)

[charliermarsh]

This came up once before, in response IIRC @MichaReiser said we should look into replacing the annotate-snippets crate which has some unusual behavior (like this).

[MichaReiser]

See rust-lang/annotate-snippets-rs#54

[charliermarsh]

Closed by #8646.