[pyupgrade] Clarify fix safety docs (UP007, UP045) (astral-sh#25288)

The current UP007 "Fix safety" paragraph reads "This rule's fix is
marked as unsafe, as it may lead to runtime errors when alongside
libraries that rely on runtime type annotations, like Pydantic, on
Python versions prior to Python 3.10..." The filer of astral-sh#17062 hit the fix
on Python 3.10+ (where the source explicitly marks the fix safe) and was
confused about what the docs were warning about.

In the thread, ntBre clarified the actual semantics ("the fix is marked
unsafe on Python versions prior to Python 3.10 but safe on and after
3.10") and pjonsson suggested flipping the sentence around. I rewrote
the paragraph to mirror the code: the fix is safe when target is 3.10+
and there are no comments, otherwise it's unsafe for one of two reasons
(pre-3.10 runtime introspection like Pydantic can `TypeError` on `X |
Y`, or comments inside the original would be dropped during rewrite).
The unusual-inner-expression caveat is kept. I applied the same rewrite
to UP045's docstring because it had the same wording.

Docstring-only. `cargo dev generate-all` and `uvx prek run --from-ref
main` both pass.

fixes astral-sh#17062

---------

Co-authored-by: Brent Westbrook <brentrwestbrook@gmail.com>

Author: 2 people

crates/ruff_linter/src/rules/pyupgrade/rules/use_pep604_annotation.rs

@@ -43,12 +43,12 @@ use crate::{Applicability, Edit, Fix, FixAvailability, Violation};
 /// while `UP045` checks for `typing.Optional`.
 ///
 /// ## Fix safety
-/// This rule's fix is marked as unsafe, as it may lead to runtime errors when
-/// alongside libraries that rely on runtime type annotations, like Pydantic,
-/// on Python versions prior to Python 3.10, or as it may remove comments if they
-/// are present within the type annotation being rewritten. It may also lead to
-/// runtime errors in unusual and likely incorrect type annotations where the type
-/// does not  support the `|` operator.
+/// This rule's fix is marked as unsafe on Python versions prior to 3.10 because
+/// using the PEP-604 syntax may lead to runtime errors in libraries that rely
+/// on runtime type annotations, like Pydantic, or in unusual and likely
+/// incorrect type annotations where the type does not support the `|`
+/// operator. The fix is also marked as unsafe when it would remove comments
+/// present within the type annotation being rewritten.
 ///
 /// ## Options
 /// - `target-version`
@@ -101,12 +101,12 @@ impl Violation for NonPEP604AnnotationUnion {
 /// ```
 ///
 /// ## Fix safety
-/// This rule's fix is marked as unsafe, as it may lead to runtime errors
-/// using libraries that rely on runtime type annotations, like Pydantic,
-/// on Python versions prior to Python 3.10, or as it may remove comments if they
-/// are present within the type annotation being rewritten. It may also lead to runtime
-/// errors in unusual and likely incorrect type annotations where the type does not
-/// support the `|` operator.
+/// This rule's fix is marked as unsafe on Python versions prior to 3.10 because
+/// using the PEP-604 syntax may lead to runtime errors in libraries that rely
+/// on runtime type annotations, like Pydantic, or in unusual and likely
+/// incorrect type annotations where the type does not support the `|`
+/// operator. The fix is also marked as unsafe when it would remove comments
+/// present within the type annotation being rewritten.
 ///
 /// ## Options
 /// - `target-version`