[pep8-naming] Fix formatting of __all__ (N816) (#20301)

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## Summary

Noticed this was not escaped when writing a project that parses the
result of `ruff rule --outputformat json`. This is visible here:
<https://docs.astral.sh/ruff/rules/mixed-case-variable-in-global-scope/#why-is-this-bad>

## Test Plan

documentation only

---------

Co-authored-by: Brent Westbrook <36778786+ntBre@users.noreply.github.com>

crates/ruff_linter/src/rules/pep8_naming/rules/mixed_case_variable_in_global_scope.rs

@@ -18,8 +18,8 @@ use crate::rules::pep8_naming::helpers;
 /// > (Let’s hope that these variables are meant for use inside one module
 /// > only.) The conventions are about the same as those for functions.
 /// >
-/// > Modules that are designed for use via from M import * should use the
-/// > __all__ mechanism to prevent exporting globals, or use the older
+/// > Modules that are designed for use via `from M import *` should use the
+/// > `__all__` mechanism to prevent exporting globals, or use the older
 /// > convention of prefixing such globals with an underscore (which you might
 /// > want to do to indicate these globals are “module non-public”).
 /// >