[flynt] add fix safety section (FLY002)

crates/ruff_linter/src/rules/flynt/rules/static_join_to_fstring.rs

@@ -28,6 +28,14 @@ use crate::rules::flynt::helpers;
 /// f"{foo} {bar}"
 /// ```
 ///
+/// # Fix safety
+/// The fix is always marked unsafe because the evaluation of the f-string
+/// expressions will default to calling the `__format__` method of each
+/// object, whereas `str.join` expects each object to be an instance of
+/// `str` and uses the corresponding string. Therefore it is possible for
+/// the values of the resulting strings to differ, or for one expression
+/// to raise an exception while the other does not.
+///
 /// ## References
 /// - [Python documentation: f-strings](https://docs.python.org/3/reference/lexical_analysis.html#f-strings)
 #[derive(ViolationMetadata)]